Why Covid boosters provide better protection against Omicron

In the race to protect their populations against Coronavirus variant Omicron, countries including the UK and the US are rolling out extensive booster programs after data showed the extra shots provided more protection against the new strain than two shots.

The latest data – from the university of Oxford – on Monday showed levels of neutralizing antibodies that attack the virus against Omicron, compared with Delta, in people who received two doses of the vaccine it developed. with AstraZeneca, or BioNTech/Pfizer injection.

The dramatic drop in antibody levels, says Oxford, “suggests that although there is no evidence of an increased likelihood of serious illness or death, there may be an increased likelihood of infection in people with infected or vaccinated”.

With initial hospital data showing that Omicron is easier to transmit compared to the dominant Delta variant, the booster looks more profitable than ever.

How do boosters work?

The Covid-19 booster vaccine familiarizes the body’s immune system with the mutated protein – the exposed part of the virus that binds to human cells. They allow the immune system to better recognize and respond to the real virus if it attacks.

According to Charles Bangham, professor of immunology at Imperial College London, boosters increase the levels of antibodies and T cells, which enhance the immune system’s response to the virus.

“The purpose of boosters is to increase the strength of antibodies and T-cell immunity, so that if you get reinfected, it becomes a trivial infection: you are less well and you are less likely to be infected. pass the disease on to others,” he said.

Teresa Lambe, the Oxford professor who helped create the university’s Covid-19 vaccine and co-authored Monday’s study, said the third dose helped “reinforce or induce a memory immune response.” stronger”.

“That means you’re in a better position for your immune response to kick in when you see the virus, so you’re better protected,” she said.

Why do they protect against Omicron so much better than two doses?

Current Covid-19 vaccines are designed to deal with the original Sars-Cov-2 strain, which first appeared in the city of Wuhan, China. But the third dose strengthens the immune system so dramatically that it creates an army of antibodies much better at killing the virus – even if it has mutated significantly.

Peter English, a former specialist with Public Health England, says boosters trigger a “rush of action” much faster and larger than the initial dose.

“A larger amount of antibodies in the blood can still neutralize some of the different variants,” he said.

Graph illustrating that English data shows a significantly increased risk of breakthrough infections with Omicron, but boosters push the risk down to Delta levels

Initial data from a laboratory trial showing that the third dose of the Pfizer vaccine resulted in a 25-fold increase in the amount of neutralizing antibodies that attack the virus against Omicron, a similar level of protection provided by the two dose against the Wuhan strain.

And UK Health Security Agency data from the ‘real world’ case of Covid-19 caused by Omicron showing the boosters offered in the UK – Pfizer and Moderna – increase protection to make them 70 to 75% more efficient than the variant .

How long does it take for the protection to take effect?

UK Health Security Data measures effectiveness two weeks after the booster trial, and Pfizer data – collected before Omicron appeared – shows that levels of antibodies against the virus , spiked seven days after the third injection.

But some suspect additional protection could come sooner than that. English says the drug that stimulates the virus that causes whooping cough has been shown to work within 48 hours. “I cannot understand why Covid-19 is so different. Enhanced response. . . can start working very quickly and produce antibodies very quickly,” he said.

Are variant-specific boosters under development?

Vaccine manufacturers have adapted their designs to prepare shots that are suitable for the Omicron variant. Pfizer said it could have the Omicron booster by March, as the mRNA technology could be used to rapidly produce a variant-specific vaccine.

But its availability generally depends on the trial period. Regulators will likely require another trial that lasts at least two months.

Penny Ward, visiting professor of pharmacy at King’s College London, said the decision to switch would depend on how well current boosters were protecting people against disease and death. and the antibody levels of those vaccinated were fine-tuned.

“If they show that boosting with the refined variant is much better than boosting with superior clinical efficacy,” she says.

Airfinity, the health analytics company, predicts that, in a best-case scenario, only 6 billion doses of an Omicron-targeted injection will be available by October 2022. If vaccine manufacturers just move half production, that target will be achieved by January 2023 at the earliest.

Will we need to push forever?

A scientific consensus has yet to emerge as to whether an annual Covid booster is needed, as is the case with the rapidly evolving influenza virus. However, while the virus is so common, it has more opportunity to mutate, creating variants that can make vaccines less effective.

Kingston Mills, professor of experimental immunology at Trinity College Dublin, predicts the need for “ad infinitum” booster shots, showing how dramatically Omicron has mutated.

“It depends a lot on how quickly we get the Sars-Cov-2 virus under control around the world,” he said. “If it mutates in unvaccinated parts of Africa, we’ll have a preference for any of those mutations.”

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