How the new bivalent Covid vaccines work


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Paris (AFP) – France on Tuesday became the latest country to approve new Covid-19 vaccines updated to target Omicron subvariants ahead of the autumn booster campaign.

Here’s what you need to know about these “bivalent” vaccines, which means they also still target the original strain that emerged in the Chinese city of Wuhan in 2019.

Mutate to avoid immunity

Two of the first vaccines developed to combat the original strain were made by the US-German team at Pfizer-BioNTech and US company Moderna, both of which use new mRNA technology.

While traditional vaccines use a weakened or inactivated germ to prepare the body for a future attack by the real virus, mRNA uses snippets of genetic material that contain instructions that tell the body’s cells how to make a protein – in this case, this famous spike protein from covid .

The body’s immune system then triggers antibodies to fight off this spike protein, readying it when the real coronavirus comes knocking.

However, the Covid virus has mutated during the pandemic and formed new spikes to evade the immune response set up by the original vaccines.

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The Omicron variant, which has milder symptoms but is more contagious, has been gaining ground around the world this year – particularly its subvariants BA.4 and BA.5 in recent months.

Vaccine manufacturers have been trying to catch up to provide updated booster shots ahead of an expected new wave of Covid cases in the Northern Hemisphere winter.

BA.4 and BA.5 are aimed for

Pfizer-BioNTech and Moderna first optimized their original vaccines to accommodate the BA.1 subvariant spike protein, while still targeting the original strain.

Then both vaccines were further optimized to accommodate the spike proteins on the BA.4 and BA.5 subvariants.

The U.S. Food and Drug Administration approved both BA.4/5 vaccines late last month, and officials there hope millions of Americans will receive bivalent booster shots throughout September.

The European Union Medicines Agency (EMA) approved Moderna and Pfizer-BioNTech’s BA.1 vaccines earlier this month.

The EMA then last week approved Pfizer-BioNTech’s BA.4/5, saying its recommendation was based on clinical data from the older BA.1 version.

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Canada, meanwhile, approved Moderna’s BA.1 vaccine in early September.

Clinical trial data remains sparse for the latest BA.4/5 vaccines, which the US has approved based on animal studies showing they elicit a stronger immune response and lower levels of virus in the lungs compared to older vaccines.

Antoine Flahault, director of the Institute of Global Health at the University of Geneva, said he was “still not convinced” of the superior efficacy of the BA.4/5 vaccines, as there have not yet been clinical trials of their effectiveness.

However, the vaccines are “very promising” and have no new safety concerns, Flahault told AFP, adding that there will be much more data in the coming weeks as the US dual-drug refresher campaign gathers momentum.

The concept of adapting a new vaccine without conducting full clinical trials every time is not new.

Influenza vaccines are updated annually and are now tetravalent, targeting components of two influenza A and two influenza B viruses.

US health officials have said that in the future, newly updated Covid booster vaccines could be recommended every year, similar to flu vaccines – unless drastically different variants emerge.

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Other bivalent vaccines

On Tuesday, the French health authority gave the green light to three bivalent vaccines – Moderna and Pfizer-BioNTech’s BA.1 vaccines and Pfizer’s BA.4/5 vaccines.

The French health agency recommended that people at risk of serious illness or caregivers receive one of the three vaccines as they become available as part of an autumn booster campaign.

France has already ordered several million doses of bivalent vaccines from Pfizer-BioNTech and Moderna, the Ministry of Health told the AFP news agency.

There are already signs of a Covid resurgence in France, where the number of cases jumped by more than 65 per cent last week after two months of decline.

Other vaccine makers are working on bivalent vaccines, including one from France’s Sanofi and Britain’s GSK, targeting the earlier Delta and Beta strains.

The EMA is reviewing this vaccine, as well as another from Spanish pharmaceutical company HIPRA, targeting the alpha and beta strains.



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