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Maddie Massy-Westropp
UNSW Medicine & Health

There has been a lot of discussion in the media about Omicron-adapted COVID-19 boosters, which are undergoing regulatory approval in several countries. The new booster vaccines, developed by Moderna and Pfizer-BioNTech, are known as 'bivalent' as they target both the original strain of the virus and the newer Omicron variant. Compared with previous COVID-19 vaccines, these boosters are reported to elicit a stronger immune response against Omicron variants.

Omicron-adapted COVID-19 boosters are likely to be part of vaccination programs in the US, UK, Canada and the European Union by the end of 2022. In Australia, Moderna's bivalent booster has now been approved for use, with Pfizer's booster also being evaluated. So what does that mean for us?

Why do we need a new COVID-19 booster targeting Omicron?

COVID-19 vaccines work by inducing neutralising antibodies, which bind to the virus spike protein and prevent it from entering host cells. The levels of these antibodies in the blood are correlated with the level of protection from infection and symptomatic disease – generally, the higher the better. 

Professor Anthony Kelleher, Director of the Kirby Institute at UNSW Sydney, says that earlier COVID-19 vaccines are slightly less effective against Omicron than the original strains of the virus, due to viral evolution. “Omicron is immunoevasive. That means it has developed mutations in the spike protein that [allow it to] help it to partially avoid the vaccine or naturally induced immune response.”

The bivalent boosters target the mutated spike protein of the Omicron variant, as well as that of the original virus strain, making immune evasion more difficult.

Should I get a COVID-19 booster now or wait for the bivalent version?

If we receive one of the bivalent vaccines, rather than one of the original vaccines, this is likely to stimulate a stronger neutralising antibody response against both Omicron and other variants that may emerge in future. However, the increase in protection against infection and illness is incremental rather than major, Dr Deborah Cromer, from the Kirby Institute, explains.

“The original vaccines provide a strong boost to people’s antibody levels and this boost acts to increase protection. The newer bivalent vaccines improve this antibody boost by about another 50 per cent. So that’s certainly something, but the main gain is from getting any booster at all.

“Neutralising antibody levels wane over time. The most important thing is, especially if it's been a reasonable period of time since a person’s last infection or last vaccination, that antibody levels get boosted. So, for sure the most important thing is getting any booster and then there are slight gains to be made from the variant-modified vaccine,” says Dr Cromer, who leads the Kirby Institute’s Infection Epidemiology and Policy Analytics Group and recently conducted a study predicting the efficacy of variant-modified COVID-19 boosters.

Will we need to keep developing new boosters?

“I think that's a possibility… You're still always going to be chasing the virus," Professor Kelleher says.

“The real game changer will be if someone can come up with a universal vaccine, that is a vaccine that can target areas of the spike protein that the virus cannot easily change. Now, whether it's possible or not, and whether that approach will be effective or not, is still to be proven and some way off. But there are certainly people working on that.”


This story was originally published on 2 September and updated on 13 September.