The increased transmissibility and possible increased severity of the Delta variant of SARS-CoV-2 underscores the importance and immediate benefits of achieving the highest possible COVID-19 vaccine uptake, especially in outbreak areas.
ATAGI suggests that several strategies could maximise first dose vaccine coverage. Achieving higher levels of first dose vaccine coverage as soon as possible, especially in those most likely to transmit SARS-CoV-2 or develop severe disease from COVID-19, complements broad and effective public health measures.
ATAGI reinforces a second dose of COVID-19 vaccine is required for durable protection and so first dose recipients should continue to be reminded to book in for their second doses.
The risk posed by the Delta Variant
ATAGI re-iterates the importance of COVID-19 vaccination as a key component of COVID-19 control with the overarching goal of protecting all people in Australia from the harm caused by SARS-CoV-2.
Outbreaks of the Delta variant have additional implications compared to previous COVID-19 outbreaks due to the original strain or other variants:
- The greater transmissibility of the Delta variant makes control of outbreaks using public health measures more difficult and increases the risk of seeding additional COVID-19 outbreaks.
- Some evidence suggests that infections with the Delta variant may be associated with more severe disease, as indicated by hospitalisations, particularly in younger people.
ATAGI reaffirms previous advice that in a large outbreak, the benefits of the COVID-19 Vaccine AstraZeneca are greater than the risk of rare side effects for all age groups.
ATAGI reiterates that all adults in greater Sydney should strongly consider the benefits of earlier protection with COVID-19 Vaccine AstraZeneca rather than waiting for alternative vaccines. ATAGI continues to recommend a shorter interval of 4 to 8 weeks between the first and second doses of COVID-19 Vaccine AstraZeneca in an outbreak (versus the routine 12-week interval that provides optimal longer-term protection) so that maximal protection against COVID-19 can be achieved earlier.
ATAGI notes the significant risk that the Delta variant poses to COVID-19 control and therefore continues to recommend COVID-19 vaccination for all adult Australians. ATAGI notes there is an increasing risk of outbreaks in places other than greater Sydney and therefore the benefits and risks may change. People considering vaccination should be informed of the changes in benefits and risks and give appropriate informed consent. People who receive COVID-19 Vaccine AstraZeneca should be aware of the symptoms of thrombosis with thrombocytopenia syndrome (TTS), and when to seek prompt medical attention. Early detection of TTS means that people can get treatment and this can improve outcomes.
Additional strategies to optimise first dose vaccine coverage
Providing a first dose of COVID-19 vaccine promptly to as many people as possible is likely to reduce hospitalisations and deaths from COVID-19. Protection against severe outcomes is substantial after a single dose of either vaccine. A first dose-prioritisation strategy has been employed in many other countries.
In addition to strict public health measures, providing a first dose of COVID-19 vaccine will contribute to interrupting transmission in affected areas. Evidence suggests that a first dose reduces symptomatic infection and transmissibility, with the protective effect starting 2-3 weeks after vaccination.
Strategies that could expand access to those in outbreak areas using available vaccine supplies include:
- Increasing the interval between first and second doses of Comirnaty (Pfizer) from 3 to 6 weeks to facilitate earlier access to first doses in areas of greatest risk of COVID-19.
- Prioritisation of any available and additional supplies of both Comirnaty (Pfizer) vaccines and COVID-19 Vaccine AstraZeneca to populations residing in areas of greatest risk of COVID-19 and those at risk of transmitting the virus.
- Addressing barriers to access to COVID-19 vaccines.
ATAGI also emphasises that for both vaccines completion of two doses is still required to attain optimal and durable protection. All people should ensure they complete a two-dose schedule.
In outbreak areas, efforts are required to address barriers to vaccination. This should include targeted communications and community engagement, education appropriate to specific populations, and vaccination centres and outreach services in accessible locations.