A field trial of Pfizer’s COVID-19 vaccine in more than half a million people confirms that it is highly effective in preventing serious illness or death, even after a single dose.
The results, released Wednesday, of a massive vaccination campaign in Israel, provide strong reassurance that the benefits of smaller, limited testing continued when the vaccine was used much more widely in a general population of varying ages and health problems.
The vaccine was 92% effective in preventing serious illness after two injections and 62% after one. The estimated effectiveness for preventing death was 72% two to three weeks after the first shot, a percentage that may improve as immunity increases over time.
It seemed just as effective in people over the age of 70 as it was in younger people.
“This is immensely reassuring … better than I imagined,” said Dr. Gregory Poland from the Mayo Clinic.
Dr. Buddy Creech of Vanderbilt University agreed, “Even after one dose, we can see very high effectiveness in preventing death,” he said.
Neither doctor played a role in the Israeli study, but both are involved in other coronavirus vaccine work.
Both doctors also said the new results could spur consideration of delaying the second shot, as the UK is trying, or giving one dose instead of two to people who have already had COVID-19, as France does. to stretch the limited stock.
“I would rather see 100 million people get one dose than 50 million people get two doses,” Creech said. “I see a lot of encouragement at one dose” in the results from Israel, published by the New England Journal of Medicine.
The vaccine, made by Pfizer and its German partner BioNTech, is given as two injections in most countries, three weeks apart.
The study was led by researchers from the Clalit Research Institute and Ben-Gurion University of the Negev in Israel, with Harvard University in the US. It did not report on the safety of the vaccine, only its effectiveness, but no unexpected problems occurred in previous tests.
Researchers compared nearly 600,000 people aged 16 and older in Israel’s largest health organization who received an injection in December or January with an equal number of people of similar age, gender and health who did not receive a vaccine. None of the participants had previously tested positive for the virus.
The vaccine was estimated to be 57% effective in preventing symptoms of COVID-19 two to three weeks after the first dose and 94% one week or more after the second dose.
The effectiveness was 74% after one injection and 87% after two for the prevention of hospitalization, and 46% and 92% for the prevention of confirmed infection. Reducing infections gives hope that the vaccine can slow the spread of the virus, but this type of research cannot determine whether this is the case.
There were 41 COVID-19-related deaths, 32 of which were in people who did not receive a vaccine.
Overall, the numbers compare well with the 95% effectiveness after two doses seen in the limited tests that led to US regulators approving emergency use of the vaccine, Poland said. How much benefit there would be from one dose was a big question, “and now there is some data” to help inform the debate, he added.
“Perhaps the right thing to do here is to protect as many people as possible … give everyone a dose as soon as possible. I think that is a very acceptable strategy to consider, ”said Poland.
Israel has now inoculated nearly half of its population. A newer variant of the virus first identified in the UK became the dominant strain in Israel during the study, so the results also provide some insight into how well the vaccine is performing against it.
Earlier this week, two UK studies suggested benefits even after one dose of the Pfizer vaccine or another from AstraZeneca. The UK is delaying the second admission for 12 weeks after the first to try to provide more people with a certain level of protection.
The Associated Press Department of Health and Science is supported by the Science Education Department of the Howard Hughes Medical Institute. The AP is solely responsible for all content.