Scotland’s vaccination program has substantially reduced Covid-19 hospital admissions, according to the results of the study released on Monday, offering the strongest real-world sign of the effectiveness of the AstraZeneca-Oxford vaccine that much of the world is counting to end the pandemic.
The study, covering the AstraZeneca and Pfizer-BioNTech vaccines, examined the number of people who were hospitalized after receiving a single dose of the vaccine. Britain has postponed the administration of the second dose for up to three months after the first, opting to offer more people partial protection from a single injection.
But the study sounded like a warning note about how long the high levels of protection from a single dose would last. The risk of hospitalization decreased after a week after people received their first injection, reaching the lowest point four to five weeks after being vaccinated. But then it seemed to rise again.
The scientists who conducted the study said it is too early to know whether the protection offered by a single dose decreases after a month, warning that more evidence is needed.
The findings in Scotland reinforced Israel’s earlier results, showing that vaccines offered significant protection against the virus. Israeli studies focused on the Pfizer vaccine, but the Scottish study extended to the AstraZeneca vaccine, administered in Britain since early January. The AstraZeneca injection is the backbone of many nations’ inoculation plans: it is much cheaper to produce and can be shipped and stored in regular refrigerators, rather than the ultracold freezers used for other vaccines.
“Both are working spectacularly well,” said Aziz Sheikh, a professor at the University of Edinburgh who participated in the study, at a news conference on Monday.
Researchers in Scotland examined about 8,000 hospitalizations related to coronavirus and studied how the risk of hospitalization differs between people who received and did not receive the vaccine. In all, more than 1.1 million people were vaccinated in the period the researchers were studying.
The number of vaccinated people who sought care at hospitals was too small to compare the AstraZeneca and Pfizer vaccines, or to give accurate numbers of their effectiveness, the researchers said.
But from 28 to 34 days after the first injection, the AstraZeneca vaccine reduced the risk of hospital admissions for Covid-19 by about 94%. In the same period, the Pfizer vaccine reduced the risk of hospitalizations by about 85 percent. In both cases, these numbers fall into a wide range of possible effects.
Because the Pfizer vaccine was authorized in Britain before the AstraZeneca injection, the researchers had more data on the Pfizer vaccine and found that protection against hospital admissions was somewhat reduced over longer periods after the first injection.
“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.
The AstraZeneca vaccine faced skepticism in parts of Europe after many countries chose not to apply it to the elderly, citing the lack of clinical trial data in that group. The Scottish study cannot give precise figures on the vaccine’s effectiveness in older people. But the combined effect of the AstraZeneca and Pfizer vaccines has substantially reduced hospital admissions in people over 80. Many elderly people received the AstraZeneca vaccine.