- Michelle Roberts
- Health publisher, BBC News online
Researchers say they see a decrease in protection against Covid-19 infections in people who have received both doses of the vaccine.
A study, conducted in the UK using real data, examines positive PCR results between May and July 2021 in more than one million people who received two doses of the Pfizer or AstraZeneca vaccine.
Protection after two doses of Pfizer increased from 88% in one month to 74% in five to six months. For AstraZeneca, the drop is 77% to 67% in four to five months.
To read especially on BBC Africa:
Although there are cases of infection in fully immunized people, vaccines still do a good job of protecting the population against the severe form of the disease and deaths from Covid-19.
Vaccines save lives
Public Health England, the UK government’s public health agency, estimates that around 84,600 deaths and 23 million infections have been prevented thanks to the Covid-19 vaccination campaign in England so far.
Professor Tim Spector of King’s College London (KCL), who led the data-driven study from epidemiological research app Zoe Covid, says these findings could explain recent infections reported by some people fully vaccinated.
“The reduction in protection is expected and is not a reason not to be vaccinated,” he said.
“Vaccines still offer high levels of protection for most of the population, especially against the Delta variant, and so we still need as many people as possible to be fully immune,” he says.
He estimates that protection against infection could drop to 50% in winter and that booster doses will be needed – but other experts urge caution in forecasting for the months ahead.
The UK is expected to start offering some people a third booster dose of the covid vaccine next month, but the government is awaiting recommendations from an independent advisory body, called JCVI, which is reviewing the evidence to support it. this decision.
“A lot of people might not need it. A lot of people may have been boosted naturally because they’ve had a natural infection with covid before, so in fact they’ll have had three vaccines,” Spector says.
“So I think that the whole should be managed with much more care than if we were content to give (the third dose) to everyone, which would be a great waste and would be ethically dubious given the resources of which we have. I think we need a more focused approach than last time, “he adds.
Simon Clarke, an expert in cell microbiology at the University of Reading, UK, explains that infection levels in the community would alter the likelihood of a person crossing (the virus) and catching the covid at some point, which makes it difficult to draw definitive conclusions about the decline in immunity.
Alexander Edwards, also from the University of Reading, says it’s important to understand when and for whom booster doses may be needed.
“Vaccination does not make people invulnerable or prevent all infections. The variants have a real and significant impact on public health, and many people still die tragically in the UK from this horrific virus.”
“The vaccines we have are remarkably safe and effective, and are still far better than other vaccines that offer enormous benefits.”
“We need to proactively plan our public health strategy to take into account imperfect protection and the possibility that protection will diminish over time,” he continues.
A similar study was released by the Office for National Statistics and the Oxford Vaccine Group last week.
Based on the results of PCR screening of nearly 400,000 people infected with the Delta variant in the UK, it showed that two doses of Pfizer vaccine were initially over 90% effective against symptomatic covid infection, against around 70% for the AstraZeneca vaccine.
But over three months, Pfizer’s protection decreased significantly, while AstraZeneca’s immunity remained more stable.
Professor Adam Finn, government vaccine consultant, explains that other studies have shown that vaccines maintain good protection against serious illness and hospitalization.
But he says: “We have to be very careful to see if this reduction (of vaccination) compared to milder diseases starts to translate into the appearance of more serious cases, because booster doses will then be necessary.”
For now, there is still no definition of the booster vaccine in Brazil, but both the Ministry of Health and the Butantan Institute (responsible for finalizing the production of CoronaVac in the country) admit that they are evaluating and are considering this possibility.