LONDON – Early studies of Britain’s mass inoculation program showed strong evidence on Monday that coronavirus vaccines were working as expected, offering the clearest signs that vaccines slow the rate of hospital admissions. from Covid-19 and may be reducing the transmission of the virus.
A single dose of the AstraZeneca or Pfizer vaccine can prevent most coronavirus-related hospitalizations, the British studies found, although the researchers said it was too early to give accurate estimates of the effect.
The findings on the AstraZeneca injection, the first to emerge outside clinical trials, represented the strongest sign yet of the effectiveness of a vaccine that much of the world depends on to end the pandemic.
And separate studies of the Pfizer vaccine offered tantalizing new evidence that a single injection may be reducing the spread of the virus, showing that it prevents not only symptomatic cases of Covid-19, but also asymptomatic infections.
The findings reinforced and went beyond studies in Israel, which also reported that the vaccine developed by Pfizer and BioNTech offered significant protection against the virus in real-world environments, and not just in clinical trials conducted last year. No other major nation is inoculating people as quickly as Britain, and it was the first country in the world to authorize and start using both the Pfizer injection and the one developed by AstraZeneca and the University of Oxford.
The studies released on Monday – two with the Pfizer injection and one with the AstraZeneca injection – showed that the two vaccines were effective against the most infectious variant of the coronavirus that has spread across Britain and has spread across the world.
“Both are working spectacularly well,” said Aziz Sheikh, a professor at the University of Edinburgh who helped conduct a study on Scottish vaccines.
Still, the findings contained some warning signs. And even when British lawmakers cited vaccine strength in announcing a gradual easing of blocking restrictions, government scientists warned that many more people needed to be injected to prevent cases from spreading to vulnerable vaccinated groups and occasionally causing illness. serious and death.
Britain decided to postpone giving people a second dose of the Pfizer and AstraZeneca vaccines until three months after the first doses, opting to offer more people partial protection from a single injection.
The trade-offs involved in this strategy were not entirely clear from the evidence released on Monday, but government scientists said that drastically reduced hospitalization rates justify the strategy.
But the findings also suggested that people were more protected from the coronavirus after a second dose. And they offered mixed answers to the question of how long the high levels of protection from a single dose would last.
“Now we need to understand the duration of this protection for a dose of the vaccine,” said Arne Akbar, a professor at University College London and president of the British Society for Immunology.
One of the new studies looked at some 19,000 health professionals in England who had received the Pfizer vaccine. Scientists were able to closely monitor whether individuals had been infected or not: they were tested regularly for the virus, regardless of whether they had symptoms or not, allowing scientists to detect asymptomatic cases.
Many of the clinical trials, on the other hand, measured only symptomatic infections.
That study showed that a single dose of the Pfizer vaccine reduced the risk of infection by approximately 70 percent. After two doses of the vaccine, protection increased to 85 percent, the scientists said, although they warned that the low number of cases makes it difficult to arrive at accurate estimates.
The Pfizer vaccine also appears to be effective in older people, who have not been so well represented in clinical trials and do not always have strong responses to vaccines. In people over 80 in England, a separate study showed that a single dose was 57 percent effective in preventing symptomatic cases of Covid-19. Protection increased to 88% after a second dose.
Older people who were vaccinated and still became ill were substantially less likely than unvaccinated people to be hospitalized or die, suggesting that the Pfizer vaccine mitigated the impact of infections even when it did not stop them entirely.
Still, some vaccinated people were hospitalized or killed by the virus, a reminder that “protection is not complete,” said Dr. Mary Ramsay, head of immunization at Public Health England.
A study conducted in Scotland covered injections by Pfizer and AstraZeneca. The results of the AstraZeneca vaccine were more limited because it was later authorized in Britain, only coming into use in early January.
The researchers examined about 8,000 hospitalizations related to the coronavirus and studied how the risk of hospitalization differs between people who received and did not receive the vaccine.
The number of vaccinated people who sought care at hospitals was so small, the researchers said, that they were only able to produce very close estimates of vaccine effectiveness and could not compare vaccines against each other.
But from 28 to 34 days after the first injection, when it appeared to be at or near peak efficacy, the AstraZeneca vaccine reduced the risk of hospital admissions for Covid-19 by about 94 percent. In the same period, the Pfizer vaccine reduced the risk of hospitalizations by about 85 percent, although in both cases the numbers were too small to be sure of the exact effect.
The findings were a reassuring signal about the effectiveness of the AstraZeneca vaccine, which is the backbone of many nations’ inoculation plans. It is much cheaper to produce and, unlike the Pfizer vaccine – and one from Moderna, which is not yet in use in Britain – can be shipped and stored in normal refrigerators.
But British studies have not been able to 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 drop in the risk of people being hospitalized started a week after they received their first injection and reached a low point four to five weeks after being vaccinated. But then it seemed to rise again.
“The peak of protection occurs in four weeks and then begins to decrease,” said Simon Clarke, a professor of cell microbiology at the University of Reading, who was not involved in the study.
In England, there was no evidence that protection levels dropped after a month. The scientists said more evidence is needed to definitively establish whether the protection offered by a single dose can decrease and how quickly.
The AstraZeneca vaccine faced skepticism in parts of Europe; many countries chose not to offer it to the elderly, citing the lack of data from clinical trials in that group.
The Scottish study cannot give precise figures on the vaccine’s effectiveness in older people. But the vaccination program has substantially reduced hospital admissions for people over 80, and many elderly people have received the AstraZeneca vaccine.