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LONDON – The first studies of the British mass inoculation program showed on Monday that the coronavirus vaccines were working as intended, offering among the clearest signs to date that the vaccines are reducing the rate of hospital admissions Covid-19 and could reduce the transmission of the virus. .
A single dose of the AstraZeneca vaccine or one made by Pfizer could prevent most coronavirus-related hospitalizations, UK studies have found, although researchers said it was too early to give precise estimates of the effect.
The results of AstraZeneca’s firing, the first to come out of clinical trials, represented the strongest signal to date of the effectiveness of a vaccine that much of the world is counting on to end the pandemic.
And separate studies of the Pfizer vaccine have offered tantalizing new evidence that a single vaccine could reduce the spread of the virus, showing that it prevents not only symptomatic cases of Covid-19, but asymptomatic infections as well.
The results strengthened and went beyond studies conducted in Israel, which also reported that the vaccine developed by Pfizer and BioNTech offered significant protection against the virus in real settings, and not just in clinical trials held there. last year. No other great nation inoculates people as quickly as Britain, and it was the first country in the world to authorize and start using both the Pfizer vaccine and the one developed by AstraZeneca and the University of Oxford .
Studies published Monday – two on the Pfizer vaccine and one on it and the AstraZeneca injection – showed that both vaccines were effective against the more infectious coronavirus variant that has taken hold in Britain and s is widespread all over the world.
“Both work wonderfully,” said Aziz Sheikh, a professor at the University of Edinburgh who helped lead a study on Scottish vaccinations.
Still, the results contained warning signs. And even as UK lawmakers have cited the strength of vaccines when announcing a gradual easing of lockdown restrictions, government scientists have warned that many more people need to be injected to prevent cases from spreading to vulnerable and vaccinated groups. and sometimes cause serious illness and death.
Britain has decided to delay administration of second doses of Pfizer and AstraZeneca vaccines for up to three months after their first doses, opting to offer more people partial protection from a single vaccine.
The trade-offs involved in this strategy were not entirely clear from the evidence released on Monday, but government scientists said sharply reduced hospitalization rates justified the strategy.
But the results also suggest that people are better protected against the coronavirus after a second dose. And they offered mixed answers to the question of how long the high levels of protection of a single dose would last.
“We now need to understand how long this protection lasts for one dose of the vaccine,” said Arne Akbar, professor at University College London and president of the British Society for Immunology.
One of the new studies looked at around 19,000 health workers in England who had received the Pfizer vaccine. Scientists were able to closely monitor whether the subjects had been infected or not: they were regularly tested for the virus whether or not they had symptoms, allowing scientists to detect asymptomatic cases.
Many clinical trials, on the other hand, have measured only symptomatic infections.
This study showed that a single dose of Pfizer vaccine reduced the risk of infection by approximately 70%. After two doses of the vaccine, protection jumped to 85%, the scientists said, while warning that the low number of cases made it difficult to make precise estimates.
The Pfizer vaccine was also shown to be effective in the elderly, who were not as well represented in clinical trials and did not always respond strongly to vaccines. In people over 80 in England, a separate study showed that a single dose was 57% effective in preventing symptomatic cases of Covid-19. Protection increased to 88% after a second dose.
Older people who had received a first dose of the vaccine and who fell ill again at least two weeks later had a significantly lower chance than unvaccinated people of being hospitalized or dying, suggesting that the Pfizer vaccine has mitigated the impact of infections even if it did not completely stop them. .
Still, some people vaccinated have been hospitalized or killed by the virus, a reminder that “protection is not complete,” said Dr Mary Ramsay, head of vaccination at Public Health England.
A study in Scotland included both Pfizer and AstraZeneca injections. Results on AstraZeneca’s vaccine were more limited as it was later cleared in Britain, not entering service until early January.
The researchers looked at around 8,000 hospital admissions linked to the coronavirus and studied how the risk of hospitalization differed between people who had and had not received a vaccine.
The number of vaccinated people who sought care in hospitals was so small, the researchers said, that they could only produce very rough estimates of vaccine effectiveness and could not compare vaccines to each other.
But from 28 to 34 days after the first injection, when it appeared to be at or near peak effectiveness, the AstraZeneca vaccine reduced the risk of Covid-19 hospitalization by about 94%. During that same period, the Pfizer vaccine reduced the risk of hospitalization by about 85%, although in both cases the numbers were too low to be sure of the exact effect.
The results were a reassuring sign about the effectiveness of the AstraZeneca vaccine, which is the backbone of many countries’ immunization plans. It’s much cheaper to produce, and unlike Pfizer’s vaccine – and Moderna’s, which is not yet in use in Britain – it can be shipped and stored in normal refrigerators.
But British studies could not determine how long the high levels of protection from a single dose of the Pfizer or AstraZeneca vaccine would last.
In the Scottish study, the decline in people’s risk of hospitalization began a week after receiving their first vaccine and reached a low point four to five weeks after being vaccinated. But then he seemed to come back up.
“Peak protection is at four weeks and then it starts to drop,” said Simon Clarke, professor of cell microbiology at the University of Reading, who was not in the study.
In England, there was no indication that protection levels had declined after one month. Scientists said more evidence was needed to definitively establish whether and how quickly the protection offered by a single dose was likely to wane.
The AstraZeneca vaccine has faced skepticism in parts of Europe; many countries have chosen not to give it to the elderly, citing a lack of clinical trial data in this group.
The Scottish study could not provide precise figures on the effectiveness of the vaccine in the elderly. But the vaccination program drastically reduced hospital admissions for people over 80, and many older people received the AstraZeneca vaccine.
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