Scotland’s vaccination program has significantly reduced Covid-19 hospital admissions, according to the results of the study released on Monday, which provides the strongest signal of the reality of the AstraZeneca-Oxford vaccine that many in the world rely on to end the pandemic .
The study, which includes both the AstraZeneca and Pfizer BioNTech vaccines, examined the number of people admitted to hospital after receiving a single dose of vaccine. Britain delayed the administration of the second dose by up to three months after the first dose, preferring to offer more people the partial protection of a single shot.
But the study sounded a warning about how long high levels of protection at a single dose would last. The risk of hospitalization decreased from one week after people received their first shot, reaching a low point four to five weeks after being vaccinated. But then it seemed to rise again.
The scientists who conducted the study said it was too early to know if the protection offered by a single dose had decreased after a month, and warned that more evidence was needed.
The findings in Scotland earlier reinforced results from Israel, which show that the vaccines provide significant protection against the virus. The Israeli studies focused on the Pfizer vaccine, but the Scottish study expanded to the AstraZeneca shot, which has been administered in Britain since early January. The AstraZeneca shot is the backbone of many countries’ vaccination plans: it is much cheaper to produce and can be shipped in normal refrigerators and not in the ultra-cold freezers used for other vaccines.
“Both work spectacularly well,” Aziz Sheikh, a professor at the University of Edinburgh who was involved in the study, told a news conference on Monday.
The researchers in Scotland examined approximately 8,000 admissions related to coronavirus-related hospitals and studied how the risk of hospitalization differs between people who have had a shot and have not received one. Overall, more than 1.1 million people were vaccinated during the period the researchers were studying.
The researchers said the number of vaccinated people cared for in hospitals was too small to compare the AstraZeneca and Pfizer vaccines, or to give exact figures for their effectiveness.
But from 28 to 34 days after the first shot, the AstraZeneca vaccine reduced the risk of ingestion in Covid-19 by about 94 percent. In the same period, the Pfizer vaccine reduced the risk of hospitalizations by about 85 percent. In both cases, the figures fit within a wide range of possible effects.
Because the Pfizer vaccine was approved in Britain before the AstraZeneca survey, the researchers had more information about the Pfizer vaccine and found that protection against hospital admissions was reduced longer after the first survey.
“The peak protection is four weeks, and then it starts to fall away,” said Simon Clarke, a professor of cellular microbiology at the University of Reading, who was not involved in the study.
The AstraZeneca vaccine has faced skepticism in parts of Europe after many countries chose not to give it to older people, citing a lack of clinical trial data in the group. The Scottish study could not provide exact figures on the efficacy of the vaccine in older people. But the combined effect of the AstraZeneca and Pfizer vaccines has significantly reduced hospital admissions in people over 80. Many older people received the AstraZeneca vaccine.