An actual test of Pfizer’s COVID-19 vaccine in more than half a million people confirms that it is very effective in preventing serious illness or death, even after one dose.
The results published today, from a mass vaccination campaign in Israel, give strong assurance that the benefits seen in smaller, limited trials continue when the vaccine is used much more widely in a general population with different ages and health conditions.
The vaccine was 92% effective in preventing serious illnesses after two shots and 62% after one. Its estimated effectiveness in preventing death was 72% two to three weeks after the first shot, a rate that may improve as immunity builds over time.
It seems just as effective in people older than 70 as in younger people.
“It’s very reassuring … better than I would have guessed,” said Dr. Gregory Poland of the Mayo Clinic said.
Dr. Buddy Creech of Vanderbilt University agrees: “Even after one dose, we can be very effective in preventing death,” he said.
No doctor played a role in the Israeli study, but both are involved in other coronavirus vaccines.
Both doctors also said the new results could increase the consideration of postponing the second shot as the UK tries, or giving one dose instead of two to people who have already had COVID-19, such as France do, to stretch limited stock.
“I’d rather see 100 million people have one dose than 50 million people have two doses,” Creech said. ‘I see a lot of encouragement for 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 shots in most countries, three weeks apart.
The study was led by researchers from the Clalit Research Institute and Ben-Gurion University in the Negev in Israel, with Harvard University in the USA. The safety of the vaccine has not been reported, but only its effectiveness, but no previous unexpected problems have arisen.
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Researchers compare nearly 600,000 people aged 16 and older in Israel’s largest health care organization who were shot in December or January with an equal number of people of the same age, gender and health who did not receive vaccines. None of the participants had previously tested positive for the virus.
The vaccine is estimated to be 57% effective in preventing any symptoms of COVID-19 two to three weeks after the first dose and 94% per week or more after the second dose.
The efficacy was 74% after one shot and 87% after two to prevent hospitalization, and 46% and 92% to prevent confirmed infection. Reducing infections gives hope that the vaccine can limit the spread of the virus, but this type of study cannot determine if this is the case.
There were 41 deaths associated with COVID-19, of which 32 were unvaccinated.
Overall, the numbers compare well with the 95% efficacy after two doses, seen in the limited tests that led to U.S. regulators approving the use of the vaccine emergency. How much benefit there would be from one dose was a big question: ‘and now there is a number of data’ to help lift the debate, he added.
‘Maybe the right thing to do here is to protect most people … to give everyone one dose as soon as possible. I think this is a very acceptable strategy to consider, “said Poland.
Israel has now vaccinated almost 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 performs against it.
Earlier this week, two UK studies suggested benefits, even after one dose of Pfizer vaccine or another than AstraZeneca. The UK is delaying the second shot until 12 weeks after the first attempt to provide more people with some protection.
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