ATAGI statement on the Omicron variant and timing of COVID-19 booster vaccination

The COVID-19 vaccines used in Australia are critical in protecting against COVID-19 due to all variants, including the newly emerged Omicron variant.

Date published:
General public


Given the likelihood of ongoing transmission of both Omicron and Delta variants, ATAGI recommends COVID-19 booster vaccination for anyone aged 18 and older who completed their primary course of COVID-19 vaccination 5 or more months ago.

Timely receipt of a booster dose is particularly important for people with increased exposure risk (e.g. occupational risk or outbreak areas) or who have risk factors for severe disease.

Either Comirnaty (Pfizer) or Spikevax (Moderna) are recommended for use as a booster vaccine, and are considered equally acceptable.

ATAGI reiterates that a third (primary) dose of COVID-19 vaccine is also recommended for anyone with immunocompromising conditions, a minimum of two months after their second dose.


ATAGI are closely examining all data on the epidemiology of COVID-19 and COVID-19 vaccine impact, in particular emerging data on the new Omicron SARS-CoV-2 variant.

On 28 October 2021, ATAGI recommended boosters for all Australians aged 18 and older from 6 months after their primary course, or from 5 months in specific circumstances. ATAGI now advises a routine interval of 5 months.

Omicron was first reported in South Africa on 24 November 2021. The World Health Organization (WHO) declared Omicron to be a SARS-CoV-2 variant of concern on 26 November 2021 and it has since been detected in over 50 countries globally. Cases of COVID-19 due to Omicron, including some acquired in Australia, have been identified in multiple Australian jurisdictions.

Evidence is still incomplete on the transmissibility, capacity to cause severe disease and overall impact of the Omicron variant. While data suggest that past infection with an earlier variant does not provide significant protection against infection, it remains unclear whether prior infection may reduce severity.1 Early data suggest that the protection provided by COVID-19 vaccination against infections with the Omicron variant is impaired compared to those with the Delta variant, but further data are required on the effectiveness against severe disease.

The virus has been isolated in several laboratories, including those in Australia, and laboratory, clinical and epidemiological studies are underway globally and in Australia to understand its potential impact. Preliminary data suggest that the increased antibody levels generated following a COVID-19 vaccine booster dose may offer improved protection against the Omicron variant. However, the correlation between antibody levels in laboratory studies and protection against infection and severe disease is not yet established.


As of the 11 December 2021, the weight of evidence suggests that a booster vaccine increases antibody levels substantially and this will likely offer protection against both Delta and the new Omicron variant. However, there is limited evidence to inform the optimal interval between primary and booster doses. Although registered for use from 6 months after primary vaccination, there are considerable data on the effectiveness and safety of boosters from 5 months from the Israeli program.2,3

The anticipated benefits of bringing forward the booster dose include earlier protection, particularly against severe disease in those at risk, and improved protection against COVID-19 due to the Omicron variant. The relative benefit of a booster vaccination increases with the duration since  primary COVID-19 vaccine course and for those living in regions with community transmission of SARS-CoV-2. There remains uncertainty about the duration of protection following a booster dose, and the potential emergence of future new variants.

Vaccine manufacturers have also signalled they are examining the need for and potential development of COVID-19 vaccines that may be more effective against new variants, however this is expected to take several months.

More information is available in ATAGI recommendations on the use of a booster dose of COVID-19 vaccine and ATAGI's Clinical guidance on COVID-19 vaccine in Australia.

Immunocompromised people have been recommended to receive  a third primary dose since 8 October 2021, two months after their second dose. Both the Pfizer and Moderna COVID-19 vaccines can be used for this third dose. ATAGI is reviewing the timing of a later dose (i.e., a post dose 3 booster dose) in this specific population and will issue advice on this in the near future. Refer to ATAGI’s statement on the use of a third primary dose of COVID-19 vaccine in individuals who are severely immunocompromised.

ATAGI will continue to review emerging evidence on the optimal interval between primary and booster COVID-19 vaccine and will provided updated advice in future as required.


  1. Pulliam, Juliet R. C., Cari van Schalkwyk, Nevashan Govender, Anne von Gottberg, Cheryl Cohen, Michelle J. Groome, Jonathan Dushoff, Koleka Mlisana, and Harry Moultrie. ‘Increased Risk of SARS-CoV-2 Reinfection Associated with Emergence of the Omicron Variant in South Africa’, 2 December 2021. Available online.
  2. Bar-On, Yinon M., Yair Goldberg, Micha Mandel, Omri Bodenheimer, Laurence Freedman, Nir Kalkstein, Barak Mizrahi, et al. ‘Protection of BNT162b2 Vaccine Booster against Covid-19 in Israel’. New England Journal of Medicine 385, no. 15 (7 October 2021): 1393–1400. Available online.
  3. Vaccines and Related Biological Products Advisory Committee October 14-15, 2021 [Meeting Presentation]. Available online. Accessed on 10 December 2021.

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