ATAGI notes that several outbreaks in Australia have now been attributed to the SARS-CoV-2 Omicron variant. With the relaxation of border restrictions in most jurisdictions, there are likely to be increasing numbers of COVID-19 cases due to the Omicron variant. In addition to the rapid spread of the Omicron variant in South Africa, this new variant is also becoming dominant in the UK and Denmark.
ATAGI notes the increasing use of booster doses of vaccine, with more than 130,000 doses administered on 16 December 2021. Approximately 1,117,020 booster doses have been delivered overall and 430,000 of those have been delivered since ATAGI recommended shortening the interval at which people become eligible between booster doses and the primary schedule bringing it forward from 6 months to 5 months on 12 December 2021.
ATAGI recognises that some flexibility may be required in recommendations for those who are due booster doses during the holiday period.
Recommendations
- At this stage, ATAGI has not changed the recommendation for commencement of eligibility of COVID-19 booster vaccination for anyone aged 18 and older who completed their primary course of COVID-19 vaccination 5 or more months ago.
- To ensure timely provision of boosters, ATAGI recommends that those who become eligible for a COVID-19 booster dose before or during the December and New Year holiday period (i.e. up to 3 January 2022) can receive them earlier than 5 months.
- ATAGI reinforces that timely receipt of a booster dose is particularly important for who have risk factors for severe disease (particularly older age and those with underlying medical conditions) or people with increased exposure risk (e.g. occupational risks or outbreak areas). ATAGI recommends that providers encourage and enable those at greatest risk to receive timely COVID-19 boosters.
- Both Comirnaty (Pfizer) or Spikevax (Moderna- 50µg) are recommended for use as a booster vaccine, and both are considered equally acceptable.
- ATAGI reiterates that a third (primary) dose of COVID-19 vaccine is also recommended for anyone with severe immunocompromise, a minimum of two months after their second dose.
ATAGI recognises that the epidemiological situation and evidence regarding boosters is evolving rapidly and will frequently review the timing of booster doses.
Rationale
Since last week, further laboratory studies have confirmed a reduction in antibody binding to the Omicron variant in post-vaccination sera. This appears to be at least partially overcome by the higher antibody concentrations in those who have received boosters 5-6 months after the primary course.1-6 UK data suggest that cases with the Omicron variant have a higher secondary crude attack rate in households than cases with the Delta variant.7 It seems likely that the rapid spread of Omicron relates to immune evasion rather than a major increase in transmissibility compared to previous strains.
A South African study noted a higher risk of reinfection due to Omicron variant than had been seen in previous waves of infection.3 Very limited data suggest that primary courses of COVID vaccines provide lower protection against infections due to Omicron than those due to Delta.8 It is noted that the UK data suggesting a higher vaccine effectiveness following booster doses are based on very small numbers of Omicron cases in vaccine recipients. There are not yet data on the age specific case-hospitalisation or case-fatality ratios (particularly in the elderly) or estimates of vaccine effectiveness against severe disease. There are not yet robust data on the safety or incremental effectiveness of booster doses if given earlier than 5 months, although small studies to date have not raised specific safety concerns.
There remain several uncertainties to inform the optimal interval between primary and booster/third doses of vaccine. The protection provided by two vaccine doses against severe disease due to Omicron is not yet clear. It remains uncertain whether a booster will provide additional protection against severe disease.
