Scotland’s vaccination program has drastically reduced hospital admissions for Covid-19, according to the results of the study released Monday, providing the strongest real-world indication of the effectiveness of the AstraZeneca-Oxford vaccine that much of the world relies on to end the pandemic.
The study, which included the AstraZeneca and Pfizer-BioNTech vaccines, examined the number of people who were hospitalized after receiving a single dose of the vaccine. Britain postponed the administration of the second dose for up to three months after the first, and chose to provide more people with partial protection from a single dose.
But the study launched a cautionary note about how long high levels of protection would last from a single dose. The risk of hospitalization decreased one week after people received their first dose, and reached a low point four to five weeks after they were vaccinated. But then it seemed to rise again.
The scientists who conducted the study said it was too early to tell whether the protection offered by a single dose diminished after a month, and warned that more evidence was needed.
Results in Scotland beefed up Previous results from Israel Vaccines have been shown to provide great protection against the virus. The Israeli studies focused on the Pfizer vaccine, but the Scottish study extended to the AstraZeneca injection, which has been administered in Britain since early January. The AstraZeneca syringe is the backbone of vaccination plans in many countries: it is much cheaper to produce, and it can be shipped and stored in regular fridges rather than the ultra-cold freezers used in other vaccines.
“They are both doing amazingly well,” Aziz Sheikh, a professor at the University of Edinburgh who participated in the study, told a news conference on Monday.
Researchers in Scotland examined nearly 8,000 hospitalizations due to the Coronavirus, and studied how the risk of hospitalization differs between people who got and did not receive an injection. Overall, more than 1.1 million people were vaccinated in the period the researchers are studying.
The researchers said the number of vaccinated people who sought hospital care was too low to compare the AstraZeneca vaccine and Pfizer, or to give accurate figures for their effectiveness.
But 28 to 34 days after the first shot, the AstraZeneca vaccine reduced the risk of Covid-19 hospitalization by nearly 94 percent. In the same time period, the Pfizer vaccine reduced the risk of hospitalization by approximately 85 percent. Either way, these numbers fit into a wide range of potential impacts.
Since the Pfizer vaccine was authorized in Britain prior to the AstraZeneca vaccine, researchers had more data on the Pfizer vaccine, and they found that protection from hospitalization decreased somewhat for longer periods of time after the first shot.
“The maximum protection level is four weeks, then it starts to regress,” said Simon Clark, a professor of cellular microbiology at the University of Reading, who was not involved in the study.
The AstraZeneca vaccine faced suspicion in parts of Europe after many countries chose not to administer it to the elderly, citing a lack of clinical trial data in that group. The Scottish study was unable to provide accurate figures about the effectiveness of this vaccine in the elderly. But the combined effect of the AstraZeneca and Pfizer vaccines has dramatically reduced hospitalization in people over the age of 80. AstraZeneca vaccine has been given to many elderly people.