Study shows decreased efficacy of Pfizer and AstraZeneca vaccines after 6 months

A survey conducted in the UK based on the results of PCR tests of more than a million people who had received both doses of vaccines from Pfizer/BioNTech or Oxford/AstraZeneca brought new evidence on the reduced effectiveness of immunizers against Covid -19 over time.

Pfizer/BioNTech’s vaccine protection against Covid-19 dropped from 88% one month after full immunization to 74% after five or six months, and AstraZeneca’s protection dropped from 77% to 67% after four or five months, according to the study.

The result adds to other research already carried out that point to a reduction in the effectiveness of vaccines over time, and heats up the debate on the need to apply a third dose of immunizing in those who have already received the two doses, while many people in the world have not even received the first.

The research was led by Professor Tim Spector, from King’s College London, and done with data from the epidemiological research application Zoe Covid. Spector told the BBC that a reduction in protection over time for immunizers was already expected and is not a reason not to get vaccinated.

“Vaccines still provide high levels of protection for the majority of the population, especially against the Delta variant, so we still need as many people as possible to be fully immunized,” he said.

Public Health England, the British government’s public health agency, estimates that the vaccination campaign in England has prevented 84,600 deaths and 23 million infections so far.

Drop in effectiveness against Delta
Another British study, carried out by Oxford University and published last week, based on the results of PCR tests on nearly 400,000 adults, had already identified a drop in the effectiveness of both vaccines against the Delta variant after three months of complete immunization.

The survey found that the effectiveness of the Pfizer/BioNTech vaccine in Delta variant infections dropped from 94% 14 days after the second dose to 78% after three months, while the effectiveness of AstraZeneca dropped from 69% to 61% in the same period. time course.

These results, in connection with evidence that the Delta variant can infect vaccinated people, who in turn can transmit the virus, reinforce the perspective that collective immunity against the coronavirus will be unattainable.

In this scenario, the population will live with the virus and the fight against Covid-19 will not be resolved like measles, for which the vaccine works for life. But vaccines will be important for infected people to develop mostly milder symptoms of the disease.

Projection of discharge in admissions
Spector, from King’s College London, estimates that the level of protection for the elderly and healthcare workers in England, who took the vaccine first, could drop to less than 50% by December, when winter begins in the northern hemisphere, and states that booster doses will be needed for part of the population.

If the infection rate remains high, encouraged by the Delta variant and relaxation of restrictions, “this scenario could mean a rise in hospital admissions and deaths,” he said.

He points out that not everyone would need the third dose, and that those who have already been infected with Covid-19, cured and received the vaccine can have a “natural boost” equivalent to having taken three doses.

“Everything will need to be managed much more carefully than just giving [a terceira dose] for everyone, which would be a huge waste and ethically dubious considering the resources we have. We need to think about a more focused approach than last time,” he said.

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