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Bivalent COVID vaccines have been in use for a few months now - here's how they're stacking up to omicron

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Vaccines have played an important role in mitigating the damage of the COVID pandemic since their rollout began just over two years ago. It is estimated that they have saved tens of millions of lives around the world.

The initial crop of COVID vaccines were designed to train our immune systems to recognize the spike protein on the surface of the original strain of SARS-CoV-2 (the virus that causes COVID-19). But, as we well know, since SARS-CoV-2 was first identified, it has continued to mutate and evolve into a variety of distinct variants.

Some of these variants carry mutations in their genomes that can increase the ability of the virus to transmit between people, escape the antibodies produced by our immune system or affect the severity of the disease.

Currently, Omicron, the main cause of COVID infections worldwide, has more than 50 mutations in its genome and is highly transmissible compared to previous variants. Some of the omicron mutations allow it to escape antibodies induced by past infections, vaccinations, and antibody therapies.

So scientists set to work designing slightly tweaked formulations of the vaccines that would target not just the original strain of SARS-CoV-2, but newer variants of the virus as well – omicron in particular. These are called bivalent vaccines.

Because they are based on the same mRNA technology used in first-generation COVID vaccines, they were able to be tested and approved quickly. But now that we’ve been using bivalent boosters in the real world for a few months now, we’re starting to gather some evidence on how well they’re working against omicron.

mRNA vaccines: an update

Both Moderna and Pfizer/BioNTech have updated their mRNA vaccines to provide broader protection. These vaccines contain small strands of genetic material known as messenger RNA that instruct our cells to make copies of the coronavirus spike protein.

Once these spike proteins are produced, they are used to train our immune cells to recognize and kill SARS-CoV-2 if we are infected. Bivalent vaccines contain two types of messenger RNA molecules that provide the instructions for two different types of virus spike protein: one from the original strain of SARS-CoV-2 and one from the omicron BA.1.

A subsequent update targets omicron BA.4 and BA.5, seeking to help our immune systems keep up with rapidly emerging omicron subvariants.

These updated bivalent vaccines were expected to train our immune system to produce antibodies that could protect against omicron and future variants that might arise.

Read more: COVID vaccine: How new ‘bivalent’ booster will target omicron

Results of safety tests indicated that Moderna’s and Pfizer/BioNTech’s bivalent vaccines were safe. Any side effects were similar to those found after vaccination with the original versions of these vaccines, such as pain at the injection site and fatigue.

Laboratory tests also showed that the bivalent vaccines elicited higher levels of micron antibodies compared to the original injections. Based on this evidence, these vaccines have received emergency approval in several regions, including the US, UK and EU.

In the UK, these bivalent vaccines began to be given to clinically vulnerable people and adults over 50 in autumn 2022.

So how well are they working?

A large US Centers for Disease Control and Prevention study looked at adults with symptomatic COVID between September and November 2022. It found that using a bivalent booster targeting the parent virus plus the BA.4/BA.5 omicron variant provided protection against symptomatic infection compared to a monovalent booster targeting only the parent strain.

Other US studies showed that the risk of hospitalization was reduced by at least 38% in people who received a bivalent booster compared to those who received two or more doses of the original vaccines. In adults over 65 years of age, additional protection reached 73%.

Meanwhile, recent research suggests that bivalent boosters will offer protection against omicron-emerging subvariants. Serum samples from people who received bivalent boosters containing BA.5 had better neutralizing activity against all omicron subvariants (especially BA.2.75.2, BQ.1.1 and XBB) than those who received one or two regular boosts.

A senior man receives a vaccination.
Coming in data on the effectiveness of bivalent vaccines is promising.
Aleksandar Malivuk/Shutterstock

What does the future hold?

Evidence so far suggests that a booster with an up-to-date bivalent vaccine is a safe and effective way to reduce the risk of serious illness and death from COVID.

It’s difficult to predict which variant will come next and when or if an updated vaccine will be needed in the future.

But mRNA vaccines are ideal for this, as they can be adapted relatively quickly to newer variants and can be produced quickly. Such is the flexibility that plans are underway to test their use as personalized vaccines in cancer patients in the UK.

Several other COVID vaccine approaches are under development to provide broader protection against current and future variants. Some are designed to stimulate our T cells, a type of immune cell. Others are made from small nanoparticles containing fragments of spike proteins from SARS-CoV-2 and several other related viruses.

Whatever the future holds, data continues to show that regardless of the type of booster used, vaccination is a safe and effective way to reduce disease transmission and protect against serious illness, hospitalization and death.