Bivalent Covid-19 vaccines: What they are and what they do

Two of the biggest Covid-19 vaccine manufacturers have produced bivalent vaccines to tackle new strains of the virus ahead of a possible spike in cases this winter. We take a look at how these work and what the experts say about their efficacy.

Since SARS-CoV-2 was detected in December 2019, there have been at least four major variants of concern (Omicron, Delta, Alpha and Beta) along with a number of subvariants.

The Omicron variant is currently the predominant strain around the world, however it has a number of subvariants (BA.1, BA.2, BA.4 and BA.5) with different levels of immune resistance. As the virus spreads it continues to mutate, and experts from John Hopkins Medicine say that new variants are appearing every week.

What are bivalent vaccines?

Pfizer-BioNTech and Moderna have each developed two vaccines that contain the original strain of the SARS-CoV2 virus and the Omicron BA.1 subvariant, and the original strain plus the Omicron BA.4 and BA.5 subvariants.

These mRNA vaccines instruct cells in the body to make the “spike” protein of the original virus strain and of the Omicron variants that cause the virus to replicate; in the case of BA.4 and BA.5 these spike proteins are identical.

These vaccinations, called “bivalent” vaccines, are now being authorized by different health regulators around the world in an attempt to tackle a potential “twindemic” of winter flu and Covid-19.

The UK was the first country to approve the use of a bivalent vaccine in August 2022, with the UK's Medicines and Healthcare Regulatory Agency (MHRA) authorizing Moderna’s vaccine for use as part of its autumn booster campaign.

Health regulators in the US, Canada, Australia, Europe, the UK and parts of Asia including Taiwan and Singapore have since approved Moderna and Pfizer-BioNTech’s bivalent vaccines.

How effective are bivalent vaccines?

Early clinical trials by Pfizer-BioNTech found that its bivalent vaccine provided a substantially higher immune response against Omicron BA.1 compared to the company’s existing vaccine. The US Food and Drug Administration (FDA) has since stated that a single booster dose of an updated bivalent vaccine is expected to provide better protection against the Omicron variant compared to older, existing vaccines.

Not everyone agrees, however. While it was hoped the updated vaccines would provide better, longer-lasting immunity, a non-peer reviewed study by Australian scientists published in August 2022 showed that bivalent vaccines offer very similar levels of protection against Omicron compared to a booster of an older vaccine. According to their research, efficacy of an updated vaccine was just 1.5 times better than that of an extra dose of the original vaccine.

Sam Fazeli, Director of EMEA Industry Research, Pharma at Bloomberg Intelligence, says this could lead to other pharma giants gaining a foot in the Covid-19 vaccine market. “The first human data for Pfizer-BioNTech and Moderna's BA.4 and BA.5 vaccines calls into question the use of bivalent shots in this booster campaign, especially against new subvariants with the lower doses used in Pfizer-BioNTech's a particular worry,” he said. “Little difference in antibody levels is shown between a bivalent booster and the original shots, potentially opening the door to competing vaccines from the likes of Sanofi and GSK.”

Vaccinations and boosters continue to be the recommended precaution for protection against the virus, especially among older people and those with compromised immunity, while continuing public health measures such as wearing high quality masks, hand-washing and avoiding large indoor gatherings are also advised. 

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