The initial COVID vaccines were designed to train our immune systems to recognise the original strain of SARS-CoV-2, the virus that causes COVID-19. But as we well know, the virus has continued to mutate into a range of variants.
As discussed before in a blog post, this emergence of multiple COVID-19 variants is being referred to as a ‘variants swarm’ or ‘variant soup’.
Some of these variants carry mutations in their genomes which can increase the virus’ ability to transmit between people, evade the antibodies produced by our immune systems, or affect the severity of the disease.
The birth of bivalent vaccines
Omicron, the major variant across the globe as of now, has been known to evade antibodies induced through prior infection, vaccination and antibody therapies.
Researchers and scientists designed vaccine formulations which would not only target the original strain of SARS-CoV-2, but also omicron. We know them as bivalent vaccines. Both Moderna and Pfizer/BioNTech have updated their mRNA vaccines to provide broader protection.
Now that we have been using bivalent boosters in the real world for a few months, there is evidence available about the bivalent’s efficacy against omicron.
So how well are they working?
A large study from the US Centers for Disease Control and Prevention looked at adults with symptomatic COVID between September and November 2022. It found that the use of a bivalent booster targeting the original virus plus the omicron BA.4/BA.5 variant provided additional protection against symptomatic infection compared with a monovalent booster targeting just the original strain.
Other US studies have shown the risk of hospitalisation was reduced by at least 38% in people who received a bivalent booster versus people who had received two or more doses of the original vaccines. In adults over 65, the additional protection was as high as 73%.
Meanwhile, recent research suggests that bivalent boosters will offer protection against emerging omicron subvariants. Serum samples from people who received the BA.5-containing bivalent boosters had better neutralising activity against all omicron subvariants (especially BA.2.75.2, BQ.1.1, and XBB) than people who received either one or two regular boosters.
What does the future hold?
The evidence so far suggests that a booster with an updated bivalent vaccine is a safe and effective way to reduce the risk of serious illness and death from COVID.
Predicting which variant will be next, and when or whether an updated vaccine will be required in the future, is difficult.
But the mRNA vaccines are ideally suited for this as they can be adapted relatively quickly to the latest variants of concern, and can be quickly produced.
Whatever the future brings, data continues to show that irrespective of the type of booster used, vaccination is a safe and effective way to reduce disease transmission and protect against serious disease.
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