A real-world 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 one dose.
The results published today, from a mass vaccination campaign in Israel, provide great assurance that the benefits seen in smaller and limited trials persisted when the vaccine was used much more widely in a general population with various ages and health conditions.
The vaccine was 92% effective in preventing serious illness after two injections and 62% after one. Its estimated effectiveness in preventing death was 72% two to three weeks after the first injection, a rate that may improve as immunity increases over time.
It seemed just as effective in people over 70 as in younger people.
“This is immensely reassuring … better than I could have imagined,” said Mayo Clinic Dr. Gregory Poland.
Dr. Buddy Creech of Vanderbilt University agreed: “Even after one dose, we can see very high effectiveness in preventing death,” he said.
Neither doctor was involved in the Israel study, but both are involved in other coronavirus vaccine work.
Both doctors also said that the new results may prompt consideration of delaying the second injection, as the UK is trying, or giving one dose instead of two to people who have already had COVID-19, as France is doing. , to stretch limited supplies.
“I’d rather see 100 million people with one dose than see 50 million people with two doses,” Creech said. “I see a lot of breath with a dose” in the Israel results, which were 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 at the Clalit Research Institute and Ben-Gurion University of the Negev in Israel, with Harvard University in the US They did not report on the safety of the vaccine, only its effectiveness, but no problems arose unexpected in previous tests.
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The researchers compared nearly 600,000 people 16 and older in Israel’s largest health care organization who received injections in December or January with an equal number of people of similar age, sex, and health who did not receive the vaccine. None of the participants had previously tested positive for the virus.
The vaccine was estimated to be 57% effective in preventing any COVID-19 symptoms two to three weeks after the first dose, and 94% one week or more after the second dose.
The efficacy was 74% after one injection and 87% after two to prevent hospitalization, and 46% and 92% to prevent confirmed infection. The reduction in infections gives hope that the vaccine can slow the spread of the virus, but this type of study cannot determine if that is the case.
There were 41 deaths related to COVID-19, 32 of them in people who did not receive the vaccine.
Overall, the numbers compare well to the 95% effectiveness after two doses that was seen in the limited evidence that led US regulators to authorize emergency use of the vaccine, Poland said. How much benefit would be obtained from one dose has been a big question, “and now there is some data” to help inform the debate, he added.
“Perhaps the right thing here to protect the greatest number of people… is to give everyone a dose as soon as possible. I think it’s a very acceptable strategy to consider, ”Poland said.
Israel has now vaccinated almost half of its population. A newer variant of the virus that was first identified in the UK became the dominant strain in Israel during the study, so the results also give an idea of how well the vaccine works against it.
Earlier this week, two UK studies suggested benefits even after a dose of the Pfizer vaccine or a different one of AstraZeneca. The UK is delaying the second injection until 12 weeks after the first to try to give more people some level of protection.
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