Immunity to Covid-19 declines at a slower rate after vaccination than previously thought, suggesting that booster shots would only be needed if a vaccine-resistant variant emerged, a senior health official said British public.

“Decline [of antibodies] may not happen as quickly as we might have anticipated, ”Dr Mary Ramsay, head of immunization at Public Health England, told MEPs on Wednesday.

The early modeling of the duration of immunity after vaccination was based on the influenza vaccine, which does not offer such high levels of protection and must be renewed every year, Ramsay added.

“We think and we assume and we can show, I hope, that these will prolong protection for several months, if not years.” It will be difficult to decide the best time to boost, but there’s no point in boosting if you are already protected, ”she said.

“If a new variant comes along and our current vaccine doesn’t work, that will be our biggest push to boost.”

The announcement that a booster shot may not be needed is likely to allay concerns about the already very limited global vaccine supply.

Earlier this month, Pfizer announced that the antibodies elicited by its injection persist for at least six months, even against some of the more worrying variants. Another study, conducted by researchers in the United States, found that the immunity provided by the Moderna vaccine lasted for a similar period.

Although data is limited beyond this period – because vaccines have only been widely used for five months – most experts believe injections are likely to provide protection for much longer.

It is believed that T cells, which can “remember” past infections and kill pathogens if they reappear, have a great influence on how long people remain resistant to infections and diseases. Some scientists believe they could provide at least some protection for up to two years after infection with Covid-19.

Ramsay, who was answering questions from Parliament’s special committee on science and technology on Wednesday, said vaccines have the potential to save more than 70,000 lives in the UK. Modeling suggests they have already prevented at least 10,400 deaths.

The risk of suffering a rare blood clotting reaction after receiving the AstraZeneca vaccine is around 1 in 100,000, said Sir Munir Pirmohamed, chairman of the Commission on Human Medicines, who has advised the UK government on the safety of drugs. vaccines.

Pirmohamed told the committee that the only risk factor for blood clotting identified so far was age, with young people at a “higher risk” for the rare side effect, which is fatal in about a fifth of cases.

He noted, however, that in India, only two cases of blood clots associated with low platelets had been identified after the administration of 100m doses of the AstraZeneca vaccine, which suggests that there may also be a factor genetic risk involved.

Work is underway to test whether administering a reduced dose of the AstraZeneca vaccine would reduce the risk of a rare clotting reaction, Pirmohamed added.

“As a pharmacologist, I strongly believe in a ‘dose-response curve’ so it’s important to look at that,” he said. “Further work is underway to understand the dose-response relationship in terms of efficacy and safety with this vaccine.”

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