Tests of the Pfizer vaccine against COVID-19 involving half a million people confirmed that it is very effective in preventing serious infections and deaths, even after the first dose.
The results of a massive vaccination campaign in Israel support those of other smaller studies, including when used extensively, among people of different ages and health problems.
The vaccine is 92% effective in preventing serious infections after two doses and 62% after one. Its effectiveness in preventing deaths is estimated to be 72% between two and three weeks after the first injection, suggesting that immunity will increase over time.
It appears to be just as effective in people over 70 as it is in young people.
“This is very reassuring. Better than we thought, ”said Mayo Clinic Director Gregory Poland.
Dr. Buddy Creech of Vanderbilt University agreed. “Even after the first dose, we noticed great effectiveness in preventing deaths,” he noted.
Neither specialist was involved in the Israel study, but both were involved in other work around the coronavirus.
Both said the new results could cause the second dose to be delayed as the UK is already testing, or to give a single dose instead of two to people who have already had COVID-19, as the French do . To vaccinate more people, bearing in mind that there are not enough vaccines for now.
“I’d rather see 100 million people on one dose than 50 million with two,” Creech said. “It’s very encouraging what you see with one dose” in the Israeli study, published Wednesday by the New England Journal of Medicine.
In most countries, two doses, three weeks apart, are given of the vaccine produced by Pfizer and the German laboratory BioNTech.
The study was led by scientists at the Clalit Research Institute and Ben Gurion University of the Negev in Israel, and Harvard University in the United States. How safe the vaccine is was not considered, just its effectiveness, but other previous studies have not shown any problems in that area.
The researchers compared nearly 600,000 people aged 16 and older who had been vaccinated in December or January with a similar number of people of similar age, gender, and health who had not been vaccinated. None of the participants had achieved positive results in the past.
The effectiveness of the vaccine in preventing COVID-19 symptoms was 57% 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 hospitalizations and 46% and 92% for the prevention of confirmed infections.
Reducing the number of infections can help prevent the spread of the virus, but this research cannot determine whether this is really the case.
There were 41 deaths related to COVID-19, of which 32 were among those who were not vaccinated.
Poland said the effectiveness of the vaccine after the first dose was one of the big questions and that “we now have some information” to consider.
“Perhaps the best way to protect as many people as possible … is to give everyone a dose as soon as possible,” said Poland. “I think it is a strategy to be considered.”
Israel has inoculated nearly half of its population. During the study, a new variant of the virus first emerged in the UK and became dominant in Israel, so the results provide some clues about the vaccine’s effectiveness against the new variant.
This week, two studies conducted in the UK also showed good results after a dose of the Pfizer vaccine and also the AstraZeneca vaccine. In Britain, the second dose takes up to 12 weeks to vaccinate as many people as possible.
The Associated Press Department of Health and Science receives assistance from the Howard Hughes Medical Institute’s Department of Science Education. The AP is responsible for the content itself.