Pfizer’s large real-world test of the COVID-19 vaccine confirms that it is highly effective in preventing serious illness or death, even after a single dose.
Real-world tests of Pfizer’s COVID-19 vaccine on more than half a million people confirm that it is highly effective in preventing serious illness or death, even after a single dose.
The vaccine was 92% effective in preventing serious illness after two injections and 62% after one injection. The estimated effectiveness for preventing death is 72% two to three weeks after the first injection, a level that can increase as immunity increases over time.
It appears to be as effective in people over 70 as it is in younger people.
“This is very convincing … better than I thought,” said Dr. Gregory Poland from the Mayo Clinic.
Dr. Buddy Creech of Vanderbilt University agrees: “Even after one dose we can see very high effectiveness in death prevention,” he said.
Neither doctor was involved in the Israeli research but both are involved in other coronavirus vaccine work.
“I’d rather see 100 million people have one dose than to see 50 million people have two doses,” Creech said. “I see a lot of encouragement for a single 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 in two injections, three weeks apart, in most countries.
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. The study did not report on vaccine safety, only effectiveness, but no unexpected problems emerged in previous testing.
The vaccine is estimated to be 57% effective at preventing COVID-19 symptoms two to three weeks after the first dose, and 94% a week or more after the second dose.
It was 74% effective after one injection and 87% after two for preventing hospitalization, and 46% and 92% for preventing confirmed infections. Reducing infections gives hope that a vaccine can curb the spread of the virus, but this type of research can’t determine if that’s the case.
There have been 41 deaths related to COVID-19, 32 of them in people who did not get the vaccine.
Overall, the figures are comparable to the 95% effectiveness after the two doses seen in the limited testing that led US regulators to authorize the emergency use of the vaccine, Poland said. How much benefit one dose will bring has been a big question, “and there is now some data” to help inform the debate, he added.
“Perhaps the right thing to do here to protect the majority of people… is to give everyone a dose as quickly as possible. I think it’s an acceptable strategy to consider, “said Poland.
Israel has now vaccinated nearly half of its population. The newer virus variant that was 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 performs against it.
Earlier this week, two UK studies suggested a benefit even after one dose of Pfizer vaccine or a different one from AstraZeneca. Britain delayed the second shot until 12 weeks after the first shot to try to give the more people some level of protection.
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