Clinical recommendations for COVID-19 vaccines

The Australian Technical Advisory Group on Immunisation (ATAGI) has made recommendations on the use of COVID-19 vaccines in Australia.

Primary vaccination course recommendations

COVID-19 vaccination is recommended for all people aged 5 years or older to protect against COVID-19. 

COVID-19 vaccination is recommended for children aged 6 months to under 5 years with severe immunocompromise, disability, and those who have complex and/or multiple health conditions that increase the risk of severe COVID-19.

For most people, a primary vaccination course consists of 2 doses.

A third primary dose is recommended for people aged 6 months or older with severe immunocompromise. See considerations for special populations: people who are immunocompromised.

Primary vaccination course: vaccine preference recommendations

Adults aged under 60 years

Pfizer, Moderna, or Novavax COVID-19 vaccines are preferred over AstraZeneca for adults aged under 60 years. It should be noted that safety and efficacy data are more limited for Novavax than for mRNA vaccines. There is a higher risk and observed severity of thrombosis with thrombocytopenia syndrome (TTS) after receiving AstraZeneca vaccine in people aged under 60 years compared with people aged 60 years or older. 

Adults aged 60 years or older

There is no brand preference for people aged 60 years and older.

People aged under 18 years

There is no brand preference for people under 18 years of age.

Pregnant women

mRNA COVID-19 vaccines (Pfizer or Moderna) are the recommended vaccines in pregnancy. There are substantial data on their safe use in pregnancy.

Novavax COVID-19 vaccine can also be used in pregnancy. There are no immunogenicity or safety data for this vaccine in pregnancy but there are no theoretical safety concerns.

AstraZeneca is not preferred in pregnancy. Pregnant women who have already received a first dose of AstraZeneca can receive an mRNA COVID-19 vaccine, AstraZeneca, or Novavax for their second dose.

Booster dose recommendations 

A single COVID-19 vaccine booster dose is recommended for all people aged 16 years and older who completed their primary course 3 or more months ago.

Children and adolescents aged 5 to 15 years in the following groups who completed their primary course 3 or more months ago may receive a single COVID-19 vaccine booster:

  • those who are severely immunocompromised
  • those who have a disability with significant or complex health needs
  • those who have complex and/or multiple health conditions that increase the risk of severe COVID-19.

For more information on boosters in children and adolescents aged 5 to 15 years see:

A second booster dose (that is a 4th dose) is recommended for people in the following groups, 3 months after the first booster dose: 

  • people 50 years or older 
  • residents aged 16 years and older of an aged care or disability care facility 
  • people aged 16 years and older who have complex, chronic, or severe medical conditions that increase their risk of severe illness from COVID-19
  • people aged 16 years and older with disability with significant or complex health needs, or multiple comorbidities that increase the risk of poor outcome from COVID-19.

People aged 30 to 49 years can receive a second booster dose of a COVID-19 vaccine, but the benefit for people in this age group is less certain. ATAGI encourages people in this age group to have a discussion with their regular medical provider to review their individual health needs and the benefits and risks of a second booster dose.

For more information on second booster doses see: Expanded ATAGI recommendations on winter COVID-19 booster doses for people at increased risk of severe COVID-19.

Booster doses are not currently recommended for children aged under 5 years, or for children aged 5 to 15 years who are not at increased risk of severe disease as defined above. Severe COVID-19 in children is uncommon and the primary course of COVID-19 vaccines generates a strong immune response. The benefit from additional doses of vaccine is likely to be small. Current evidence does not suggest that booster doses are needed at this time.

Booster dose: vaccine preference recommendations

For people aged 5 to 17 years, Pfizer COVID-19 vaccine is the only vaccine registered for use as a booster.

For people aged 18 years and older, Pfizer, Moderna original or Moderna bivalent COVID-19 vaccines are the preferred vaccines for a booster dose, regardless of which vaccine was used for the primary course.

Although not preferred, AstraZeneca or Novavax COVID-19 vaccines can be used as a booster dose in people aged 18 years and older in the following circumstances:

  • people who have a contraindication to mRNA vaccines (including those who have had a serious adverse event following mRNA vaccines, such as a history of anaphylaxis or myocarditis attributed to an mRNA vaccine)
  • people who do not prefer an mRNA vaccine

Although not TGA-registered as a booster in this age group, Novavax can be used as a booster in people aged 12 years or older if no other COVID-19 vaccine brand is suitable for that person.

There is a growing body of evidence supporting the safety and effectiveness of Pfizer and Moderna as booster vaccines. Data on the use of AstraZeneca as a booster dose are more limited (see COVID-19 Vaccine information). There are very limited data on the use of Novavax as a booster.

Booster dose: recommended intervals

The recommended interval between completing the primary COVID-19 vaccine course (the second dose for most people and vaccine brands) and the first booster dose is 3 months.

The recommended interval between the first booster dose and a second booster dose (for those who are recommended to receive a second booster dose) is 3 months. 

There is no upper time limit for the administration of a booster dose. However, vaccine effectiveness wanes over time, and timely receipt of boosters is encouraged for people aged 16 years and older.

The evidence underpinning booster dose recommendations will continue to be reviewed and this clinical guidance may be refined. For more details see: COVID-19 vaccine information.

For more information on booster doses, see:

Considerations for special populations

People who are immunocompromised

COVID-19 vaccine is recommended for people who are immunocompromised because of their increased risk of severe illness with COVID-19.1

Vaccinated immunocompromised people should be advised to continue taking other protective measures against SARS-CoV-2.

Immunocompromise – additional primary dose

A third primary dose of COVID-19 vaccine is recommended for all people aged 6 months or older with severe immunocompromise who are receiving a 2-dose primary course. The third dose should be given from 2 months after the second vaccine dose.

The third dose is intended to address the risk of lowered response or non-response to the standard 2-dose schedule. For more details on vaccine effectiveness in people who are immunocompromised, see COVID-19 vaccine product information.

An age-appropriate formulation of an mRNA COVID-19 vaccine (Pfizer or Moderna) or the Novavax COVID-19 vaccine (for people aged ≥ 12 years) is recommended for the third dose (see also: Recommended and variations on vaccine schedule for vaccines recommended in each age cohort). Most studies of third doses of COVID-19 vaccine in immunocompromised people have used mRNA vaccines.

There is very limited evidence of the efficacy of Novavax in immunocompromised people.

The AstraZeneca COVID-19 vaccine is not preferred but can be used for the third dose in adults if there are contraindications to mRNA and Novavax COVID-19 vaccines.

More information, including definitions of severe immunocompromise, is available in:

Immunocompromise – booster doses

Severely immunocompromised people aged 5 to 15 years who have received a third primary dose may receive a booster dose (a fourth dose) 3 months after the primary course, in line with the general population.

Second booster doses for people aged under 16 years are not currently recommended.

Severely immunocompromised people aged 16 years or older who have received a third primary dose are recommended to receive a first booster dose (a fourth dose) 3 months after the primary course, and a second booster dose (a fifth dose) 3 months after the first booster.

Children and adolescents

COVID-19 vaccination is recommended for all children and adolescents aged ≥5 years, and for children aged 6 months to <5 years who are at greatest risk of severe COVID-19.

The dose and concentration vary between the different age-specific COVID-19 vaccine formulations. Children should be given a formulation that is registered for their age. Providers should be vigilant about the potential for dosing errors, including overdosing, with COVID-19 vaccines in children.

Children aged 6 months to <5 years

The Moderna COVID-19 6 month 5 years formulation (blue cap, purple stripe vial 100 µg/mL) is given as a 2-dose primary schedule, with 25 µg of mRNA in each 0.25 mL dose.

ATAGI recommends COVID-19 vaccination for children in this age group who are at greatest risk of severe outcomes from COVID-19. 

These include children with the following or similar conditions:

  • severe primary or secondary immunodeficiency, including those undergoing treatment for cancer, or on immunosuppressive treatments as listed in the ATAGI advice on 3rd primary doses of COVID-19 vaccine in individuals who are severely immunocompromised
  • bone marrow or stem cell transplant, or chimeric antigen T-cell (CAR-T) therapy
  • complex congenital cardiac disease
  • structural airway anomalies or chronic lung disease
  • type 1 diabetes mellitus
  • chronic neurological or neuromuscular conditions
  • a disability with significant or complex health needs, such as severe cerebral palsy or Down syndrome (trisomy 21).

ATAGI does not currently recommend COVID-19 vaccination for children in this age group who are not in the listed high-risk categories for severe COVID-19.

The Moderna COVID-19 paediatric formulation (blue cap vial, 100 µg/mL) is the only vaccine available for use in this age group, at a dose of 25 µg in 0.25 mL.

For more information see: ATAGI recommendations on COVID-19 vaccine use in children aged 6 months to under 5 years.

Children aged 5 to 11 years

The following vaccines are available for children in this age group:

The Pfizer COVID-19 5-11 years formulation (orange cap vial), which  contains 10 µg per 0.2 mL dose. The Moderna COVID-19 6 months to 5 years formulation (blue cap, purple stripe vial; 100 µg/mL) is available for children aged 5 years, and is given as a 2-dose primary schedule, with 25 µg of mRNA in each 0.25 mL dose. The Moderna 6-11 years formulation (red cap vial; 200 µg/mL) is available for children aged 6 to 11 years, who receive half the adult dose (50 µg in 0.25 mL).It is preferable to complete the primary course with the same brand of vaccine, rather than a different brand. However, children should receive the appropriate formulation and dose of vaccine according to their age on the day of vaccination. See Special circumstances for mixed schedules. Adverse events after the Moderna vaccines in young children are usually mild to moderate and transient, but may be more common than adverse events after the paediatric Pfizer vaccines. For more information, see COVID-19 vaccine adverse events.

Adolescents aged 12 to 17 years

Pfizer, Moderna and Novavax COVID-19 vaccines are registered for use in people aged 12 years or older.

There are limited data on the safety and immunogenicity of Novavax compared with mRNA vaccines (Pfizer or Moderna).

The AstraZeneca COVID-19 vaccine is only registered in people aged 18 years and older. If AstraZeneca is inadvertently given as a first dose to a person aged under 18 years, Pfizer, Moderna or Novavax should be used for the second dose.

Only Pfizer is currently registered as a booster dose for adolescents 12 to 17 years.

More details on vaccination for children and adolescents

For more information see:

Pregnancy, breastfeeding or planning pregnancy

mRNA vaccines (Pfizer or Moderna) are the recommended COVID-19 vaccines for pregnant women. This is based on the growing body of evidence supporting the safety of mRNA vaccines in pregnancy. Data are still very limited on the safety of the other COVID-19 vaccines (AstraZeneca and Novavax) in pregnancy. However, people who cannot access an mRNA vaccine can consider vaccination with AstraZeneca or Novavax if the benefits to the individual outweigh the potential risks.

Women aged 16 years or older who are pregnant and had their primary course at least 3 months ago are recommended to receive a booster dose. Pfizer or Moderna (original or bivalent) are the preferred brands for the booster dose, regardless of the brand that was given for the primary course.

Pregnant women aged 30 years and older may receive a second booster dose (a fourth dose) of COVID-19 vaccine. ATAGI does not specifically recommend a second booster dose for healthy adults aged 30 to 49 years but encourages people in this age group to have a discussion with their regular medical provider to review their individual health needs and consider the benefits and risks of a second booster dose.

There are no studies on second booster doses in pregnant women, and limited experience from vaccination programs, but there are no theoretical safety concerns.

For more details, see Shared decision making guide for women who are pregnant, breastfeeding or planning pregnancy.

For details on:  

People with a past SARS-CoV-2 infection

All people are recommended to defer COVID-19 vaccination for 3 months after a confirmed SARS-CoV-2 infection. The next scheduled dose should then be given as soon as possible. All recommended doses should still be received and no doses should be omitted from the schedule.

This advice may change if future variants of SARS-CoV-2 emerge. The risk of reinfection with the Omicron variant is very low within the first 3 months following a confirmed infection.2 The Delta variant is no longer circulating in Australia.

Vaccination is likely to enhance the protection induced by infection. The interval between infection and vaccination enhances the protection from vaccination by further boosting the immune response, including immune memory response, generated following infection.3

A person may be vaccinated earlier than the recommended 3-month interval in exceptional circumstances, such as before starting an immunosuppressant, before overseas travel or if someone cannot reschedule vaccination easily (such as in an outreach vaccination program).

Infection can be confirmed by either PCR or rapid antigen test. Results of rapid antigen tests should be reported to jurisdiction reporting systems (where applicable). 

For people who have been infected and are required to receive COVID-19 vaccination, a temporary medical exemption may be applicable. People should speak with their healthcare provider about what is best for them. Providers are advised to only provide temporary exemptions for a period of up to 4 months after infection. This is due to the increased risk of reinfection after this time. 

People who were previously vaccinated within 3 months of a confirmed SARS-CoV-2 infection do not need to repeat any doses.  

People who have been infected with SARS-CoV-2 can receive other (non-COVID) vaccines without any minimum interval. As with any vaccine, vaccination should be deferred in people who are acutely unwell (such as with an acute febrile or systemic illness). 

People treated with an anti-SARS-CoV-2 monoclonal antibody 

Anti-SARS-CoV-2 monoclonal antibodies can be used to treat SARS-CoV-2 infection, or as pre- or post-exposure prophylaxis. 

When monoclonal antibodies are used as treatment for COVID-19 (that is, after infection with SARS-CoV-2), the recommended interval for a booster dose of COVID-19 vaccine is 3 months (the same as for the interval after infection). Also see People with a past SARS-CoV-2 infection.

When monoclonal antibodies are used as pre- or post-exposure prophylaxis to prevent COVID-19 (currently only tixagevimab and cilgavimab – Evusheld), there is no minimum recommended interval, and the timing of vaccination is a clinical decision. Providers should consider several factors, including the following:

  • There is a theoretical risk of interference between antibody treatments and vaccines.
  • Monoclonal antibodies are likely to protect the person for at least 2 to 3 months, so the incremental benefit of a booster soon after treatment may be small.
  • There are no known concerns regarding adverse events if there is a short interval between tixagevimab/cilgavimab and vaccine.
  • Consider whether the person is likely to return for a booster dose at a later date.

As with all vaccines, COVID-19 vaccination should be deferred in people who are acutely unwell.

Timing of administration of other vaccines

COVID-19 vaccines can be co-administered in children aged 6 months to <5 years if separation of vaccines would be logistically challenging. However, where possible, it is preferable to separate administration of Moderna (6 months to 5 years formulation) paediatric COVID-19 vaccine from other vaccines by 7 to 14 days. Limited data are available on co-administration in this age group, but co-administration may lead to higher rates of adverse events, including fever.

For people aged 5 years and older, COVID-19 vaccines can be co-administered (that is, given on the same day) with an influenza vaccine. Studies demonstrate the safety and immunogenicity of co-administration of COVID-19 and influenza vaccines.COVID-19 vaccines can also be co-administered with other vaccines if required. This includes routine childhood and adolescent vaccines. The benefits of ensuring timely vaccination and maintaining high vaccine uptake outweigh any potential risks associated with immunogenicity, local adverse reactions or fever.

There is limited evidence on the safety and effectiveness of co-administering COVID-19 vaccines at the same time as other vaccines. Providers need to balance the opportunistic need for co-administration with the benefits of giving the vaccines on separate visits. There is the potential for an increase in mild to moderate adverse events when more than one vaccine is given at the same time. Co-administration or near administration (e.g., within days) with another vaccine may also make it challenging to attribute potential adverse events.4,5 Providers should ensure that parents/guardians of young children receiving COVID-19 vaccines are aware of the increased potential for local reactions.

Co-administration of antipyretics or analgesics

Using paracetamol or ibuprofen before receiving a COVID-19 vaccine is not recommended.

Pain relievers such as antipyretics and analgesics can be taken after vaccination if needed to manage vaccine-related side effects such as fever and myalgia.

Recommended and variations on primary vaccination schedule

COVID-19 vaccine dosing interval for children aged 6 months to<5 years

ATAGI recommends a dosing schedule for Moderna  6 months to 5 years formulation of 2 doses, 8 weeks apart.

The manufacturer’s recommended dosing schedule for the Moderna 6 months to 5 years formulation vaccine is 2 doses, 4 weeks apart.

ATAGI’s recommended longer dosing interval will allow more time to observe international data on potentially rare adverse events in this age group. It may also improve immunogenicity. In adult populations, extending the interval to 8 weeks or longer has resulted in higher antibody levels, improved vaccine effectiveness and potentially longer duration of protection compared with the standard interval.6-8 Extended dosing intervals have not yet been directly studied in children.

Shorter dose intervals

The dose interval for paediatric Moderna formulations can be shortened to a minimum of 4 weeks.

The benefits of earlier protection should be weighed against the benefits of the longer dose interval, such as a slightly lower risk of adverse events and a longer duration of protection.

Shortening of the recommended dose interval below the manufacturer’s dosing schedule may result in a suboptimal immune response.

Longer dose intervals

If the second dose of paediatric Moderna vaccines is administered later than the recommended interval, no further doses are recommended.

COVID-19 vaccine dosing interval for children aged 5 to 11 years

ATAGI recommends a dosing schedule for Pfizer 5 to 11 years formulation or Moderna 6 to11 years formulation  of 2 doses, 8 weeks apart. The manufacturer’s recommended dosing schedule for Pfizer 5 to 11 years formulation is 2 doses, 3 weeks apart; and for Moderna 6 to 11 years formulation is 2 doses, 4 weeks apart.

ATAGI’s recommended longer dosing interval will allow more time to observe international data on potentially rare adverse events in this age group. It may also improve immunogenicity. In adult populations, extending the interval to 8 weeks or longer has resulted in higher antibody levels, improved vaccine effectiveness and potentially longer duration of protection compared with the standard interval.6-8 Extended dosing intervals have not yet been directly studied in children. This recommendation is consistent with other national immunisation technical advisory groups, such as the National Advisory Committee on Immunization in Canada.9

Also see: Mixed (heterologous) schedules.

Shorter dose intervals

The dose interval for Pfizer 5 to 11 years formulation can be shortened in special circumstances to a minimum of 3 weeks, for higher risk groups (such as those with medical risk factors for severe illness) or before international travel.

The dose interval for  Moderna 6 to 11 years formulation can be shortened in the same special circumstances to a minimum of 4 weeks.

The benefits of earlier protection should be weighed against the benefits of the longer dose interval, such as a slightly lower risk of adverse events and a longer duration of protection.

Shortening of the recommended dose interval below the manufacturer’s dosing schedule may result in a suboptimal immune response.

Longer dose intervals

If the second dose of  Pfizer 5 to 11 years formulation or the second paediatric dose of Moderna 6 to 11 years formulation is administered later than the recommended interval, no further doses are recommended.

Pfizer and Moderna COVID-19 vaccine dosing interval for adolescents and adults  aged 12 years and older

ATAGI recommends a primary dosing schedule of the Pfizer ≥12 years vaccine or the Moderna  ≥12 years vaccine of 2 doses, 8 weeks apart. The manufacturer’s dosing schedule for Pfizer ≥12 years is 2 doses, at least 21 days (3 weeks) apart; and for Moderna  ≥12 years, 2 doses, 4 weeks apart.

The extended dosing interval of 8 weeks may improve vaccine effectiveness. The longer interval may also reduce the risk of myocarditis and pericarditis, particularly for those most at risk of these side effects (males, aged 12 to 39 years).

For more information see: ATAGI guidance on myocarditis and pericarditis after mRNA COVID-19 vaccines.

Although Pfizer and Moderna may provide partial protection against COVID-19 as soon as 12 days after the first dose, this protection is likely to be short lived. A 2-dose course is recommended for optimal protection. 

Shorter dose intervals

The dosing interval can be shortened to a minimum of 3 weeks for Pfizer ≥12 years or 4 weeks for Moderna ≥12 years. This shorter interval can be used in specific circumstances for higher risk groups (such as older people of those with medical risk factors for severe illness), or before international travel.

Providers should consider the potential risk of myocarditis and pericarditis when selecting a COVID-19 vaccine brand and dose interval, taking into account the person’s age, preferences and any precautions to specific vaccine brands.

Shortening of the recommended dose interval below the manufacturer’s dosing schedule may result in a suboptimal immune response.

For more information, see use of an additional COVID-19 vaccine dose as a replacement dose if the second dose was given less than 14 days after the first dose.

Longer dose intervals

If the second dose of Pfizer or Moderna is administered later than the recommended interval, no further doses are recommended.

AstraZeneca COVID-19 vaccine dosing interval

The recommended interval between 2 doses of the AstraZeneca COVID-19 vaccine is 12 weeks.

The minimum interval between doses is 4 weeks.

The duration of protection after a single dose of AstraZeneca has not yet been established. A second dose is recommended for optimal protection.

Shorter dose intervals

Shortening of the recommended dose interval may result in a suboptimal immune response.

It is acceptable to shorten the interval between doses from 12 weeks to no less than 4 weeks. This may be appropriate in certain circumstances – for example, imminent travel or anticipated risk of SARS-CoV-2 exposure.

In an outbreak setting, ATAGI recommends an interval of 4 to 8 weeks between doses.

In clinical trials, the timing of administration of AstraZeneca ranged from around 4 weeks to up to 26 weeks. In a post-hoc analysis, vaccine efficacy after the second dose of AstraZeneca progressively increased with a longer interval between doses.10

Also see vaccine information – clinical guidance for more details.

For more information, see Use of an additional COVID-19 vaccine dose as a replacement dose if the second dose was given less than 14 days after the first dose.

Longer dose intervals

If the second dose of AstraZeneca COVID-19 vaccine is administered later than the recommended interval, no further doses are required.

Novavax COVID-19 vaccine dosing interval

ATAGI recommends a primary dosing schedule of Novavax COVID-19 vaccine of 2 doses, 8 weeks apart. The manufacturer’s dosing schedule for Novavax is 2 doses, at least 21 days (3 weeks) apart.

The extended dosing interval of 8 weeks has been selected to be consistent with recommendations for other COVID-19 vaccines. There is currently no evidence on extended dosing intervals for Novavax. But, evidence from other COVID-19 vaccines has suggested that a longer dosing interval may improve vaccine effectiveness. The longer dose interval may also reduce the risk of myocarditis and pericarditis, particularly for those most at risk of these adverse events (males aged 12 to 39 years).

The duration of protection after a single dose of Novavax has not yet been established. A second dose is recommended for optimal protection.

Shorter dose intervals

The dosing interval can be shortened to a minimum of 3 weeks. This shorter interval can be used in specific circumstances for higher risk groups (such as older people of those with medical risk factors for severe illness), or before international travel.

Shortening of the recommended dose interval may result in a suboptimal immune response.

For more information, see Use of an additional COVID-19 vaccine dose as a replacement dose if the second dose was given less than 14 days after the first dose.

Longer dose intervals

If the second dose of Novavax is administered later than the recommended interval, no further doses are recommended.

Minimum valid dose schedules

ATAGI advises that the absolute minimum interval between the first and second dose of any COVID-19 vaccine is 14 days.  Dose intervals of at least 14 days are considered acceptable and valid, and the person will be considered fully vaccinated in the Australian Immunisation Register (AIR).

Use of an additional COVID-19 vaccine dose as a replacement dose if the second dose was given less than 14 days after the first dose 

A second dose of a COVID-19 vaccine administered <14 days after the first dose is considered an invalid dose. An additional COVID-19 vaccine dose should be administered as a replacement dose.

The aim of this replacement dose is to attain a level of immune response that is comparable to that expected after completing a 2-dose primary course of a COVID-19 vaccine according to the recommended dosage and schedule.

The same COVID-19 vaccine brand should be used for the replacement dose to complete the primary vaccination course, unless there are special circumstances indicating the use of an alternative vaccine. See Mixed (heterologous) schedules

The interval between the invalid second dose and the replacement dose is flexible but is recommended at 4 to 12 weeks after the invalid second dose. Timing of the replacement dose should be informed by an individual risk-benefit assessment that considers:

  • risk of exposure to SARS-CoV-2 – for example, workers in health care, aged care, disability care, border and quarantine facilities may warrant vaccination with a replacement dose sooner 
  • local disease epidemiology
  • mandatory vaccination requirements for work (such as aged care or healthcare workers)
  • individual medical conditions associated with increased risk of severe COVID-19 (such as immunocompromise).

There are no direct clinical trial data on vaccines used in Australia regarding a second dose being administered at <14 days after the first dose. The recommendation for a replacement dose is based on first principles. It takes into consideration the small amount of preliminary data in trials where participants received a third dose of the vaccine (at various intervals), and the potential incremental benefits outweighing the potential adverse effects. 

These recommendations do not apply to booster doses.

Mixed (heterologous) schedules

It  is preferable to use the same brand of COVID-19 vaccine for the primary course.  

An alternative vaccine brand for dose 2 (that is registered for the appropriate age group) should be used if:

  • there are specific medical contraindications or precautions to the first-dose brand
  • the same vaccine brand is not available in Australia
  • the person is unable to access the same brand or does not accept a second dose of the same brand.  

Emerging data support the safety and efficacy of mixed schedules. 

Mixed schedules of Therapeutic Goods Administration (TGA)-approved or TGA-recognised vaccines are acceptable.

The recommended interval between first and second doses of a mixed schedule is 4 to 12 weeks after the first dose, regardless of the brand of the first dose. An interval longer than 12 weeks is acceptable if the second dose cannot be administered during this time window.

Short-term adverse reactions are slightly more likely to occur in people who have a different vaccine for dose 2 than if they had the same vaccine for both doses, but the nature and severity of the adverse effects are similar.11-17

Emerging data show that mixed schedules stimulate an adequate or comparable immune response compared with using the same brand for both doses. These trials have mostly been conducted with AstraZeneca COVID-19 vaccine as dose 1 and either Pfizer or Moderna COVID-19 vaccine as dose 2. One randomised controlled trial with 100 participants used Pfizer as the first dose followed by AstraZeneca as the second dose. These studies also showed an acceptable safety profile in the small cohorts vaccinated with mixed schedules.11,14,15,17-19

Results from studies investigating mixed schedules of only mRNA vaccines (Pfizer and Moderna) in a primary course is limited. Preliminary results from a Canadian observational cohort study in people aged ≥65 years found no significant differences in antibody responses 4 weeks after the second dose of Pfizer following a first dose of Moderna, compared with those who received the same vaccine for both doses. Reactogenicity was not reported in this study.20

One study investigated AstraZeneca as the second dose following a first dose of an mRNA vaccine. This study showed that the immune response after a first dose of Pfizer followed by AstraZeneca was lower than two doses of Pfizer.11

Currently there are no data showing the efficacy or safety of mixed doses using the Novavax vaccine for one of the doses. However, there are no theoretical concerns about the safety of mixed doses with Novavax.

Special circumstances for mixed schedules

In the following special circumstances, an alternative formulation, brand or vaccine platform may be recommended for the second dose (if not contraindicated).

Children who turn 6 (Moderna vaccine) or 12 (either brand) after their first dose of vaccine

Children should receive the appropriate brand and dose of vaccine according to their age on the day of vaccination.

For example:

  • children who turn 6 after receiving their first dose of the Moderna 6 months to 5 years formulation (25 µg of mRNA per dose) should receive half the adult dose of Moderna for their second dose (50 µg of mRNA per dose), as recommended for children aged 6 to 11 years
  • children who turn 12 after their first dose of Pfizer 5 to 11 years or Moderna 6 to 11 years should receive the  Pfizer ≥12 years or Moderna ≥12 years formulation to complete the primary course.

People with serious vaccine-attributable adverse events after dose 1 that warrant the use of an alternative vaccine brand for dose 2

Serious vaccine-attributable adverse events include:

  • anaphylaxis to the first dose of a COVID-19 vaccine (note: anaphylaxis to a previous dose of an mRNA COVID-19 vaccine (Pfizer or Moderna) is a contraindication to further doses of either vaccine), OR  
  • thrombosis with thrombocytopenia following the first dose of AstraZeneca, OR
  • any other serious adverse event attributed to a previous dose of a COVID-19 vaccine (and without another cause identified) that:
    • has been reported to State or Territory adverse event reporting programs and/or the TGA, AND
    • has been determined to be serious following review by, and/or on the opinion of, an experienced immunisation provider/medical specialist taking into account whether repeat vaccine doses would be associated with a risk of recurrence of the serious adverse event.

Assessment of adverse events following immunisation requires detailed information about the event and the severity of the condition, as well as a determination of the likelihood of a causal link with vaccination. Serious adverse events are generally defined as those which:

  • require hospitalisation (for example, thrombosis with thrombocytopenia following the first dose of AstraZeneca)
  • are medically significant (for example, immune thrombocytopenia purpura, myocarditis)
  • are potentially life-threatening (for example, anaphylaxis), and/or
  • result in persistent or significant disability (for example, Guillain-Barré syndrome).

These reactions do not typically include expected local or systemic reactions that are known to occur within the first few days after vaccination. Attributing a serious adverse event to a previous dose of a COVID-19 vaccine may require discussion with the person’s GP, local immunisation service or relevant medical specialist.

People with a precautionary condition for which the use of an alternative COVID-19 vaccines is recommended instead of AstraZeneca

Precautionary conditions for AstraZeneca are:

  • history of cerebral venous sinus thrombosis (CVST)
  • history of heparin-induced thrombocytopenia (HIT)
  • history of idiopathic splanchnic (mesenteric, portal, splenic) venous thrombosis
  • history of anti-phospholipid syndrome (APLS) with thrombosis.

People given an incomplete course of a COVID-19 vaccine brand that is not available in Australia

People who received a first dose of a COVID-19 vaccine overseas that is not available in Australia can be offered an alternative vaccine brand available in Australia to complete their primary vaccination course.  

The TGA has information on vaccines that are recognised for the purposes of travel to Australia. People who have had a first dose of a vaccine that is not recognised by the TGA (or are unable to provide evidence of previous vaccine doses) should restart the primary vaccination course using a TGA approved or recognised vaccine. It is recommended that the new primary vaccination course commences 4 to 12 weeks after the last vaccine dose.

Further reading

  1. Gao Y, Chen Y, Liu M, Shi S, Tian J. Impacts of immunosuppression and immunodeficiency on COVID-19: a systematic review and meta-analysis. Journal of Infection 2020;81:e93-e5.
  2. Chemaitelly H, Ayoub HH, Coyle P, et al. Protection of Omicron sub-lineage infection against reinfection with another Omicron sub-lineage. medRxiv 2022;2022:02.24.22271440.
  3. Altarawneh H, Chemaitelly H, Ayoub HH, et al. Effect of prior infection, vaccination, and hybrid immunity against symptomatic BA.1 and BA.2 Omicron infections and severe COVID-19 in Qatar. medRxiv 2022;2022:03.22.22272745.
  4. Lazarus R, Baos S, Cappel-Porter H, et al. The safety and immunogenicity of concomitant administration of COVID-19 vaccines (ChAdOx1 or BNT162b2) with seasonal influenza vaccines in adults: a phase IV, multicentre randomised controlled trial with blinding (ComFluCOV). 2021. (Accessed 28 October 2021). https://ssrn.com/abstract=3931758
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