Testing 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 mass vaccination campaign in Israel support those of other smaller studies, also when it is widely used, among people of different ages and health conditions.
The vaccine is 92% effective in preventing serious infections after two doses and 62% after one. It is estimated that its effectiveness in preventing deaths is 72% between two and three weeks after the first injection, which suggests that immunity will increase over time.
It appears to be as effective in people over 70 as it is in the young.
“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 a great effectiveness in preventing deaths,” he commented.
Neither specialist was involved in the Israel study, but both have been involved in other work on the coronavirus.
Both said the new results may cause the second dose to be delayed, as the UK is already testing, or a single dose instead of two given to people who already had COVID-19, as the French do. in order to vaccinate more people, taking into account that for now there are not enough vaccines.
“I’d rather see 100 million people with one dose rather than 50 million with two,” Creech said. “It’s very encouraging what you see with a dose” in the Israeli study, which was published Wednesday by the New England Journal of Medicine.
Effectiveness of the vaccine
In most countries, two doses are given, three weeks apart, of the vaccine, produced by Pfizer and the German laboratory BioNTech.
The study was led by scientists from 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, only its effectiveness, but previous studies revealed no problems in that area.
The researchers compared nearly 600,000 people aged 16 and over, who were vaccinated in December or January, with a similar number of people of similar age, sex and health who had not been vaccinated. None of the participants had had positive results in the past.
In addition, the vaccine’s effectiveness in preventing COVID-19 symptoms was 57% two to three weeks after the first dose; and 94% one week or more after the second.
The effectiveness was 74% after one injection and 87% after two in the prevention of hospitalizations and; 46% and 92% in the prevention of confirmed infections.
Reducing the number of infecions
Reducing the number of infections can help prevent the spread of the virus; but this study cannot determine if this is really the case.
There were 41 deaths associated with COVID-19, 32 of them among those who did not get vaccinated.
Moreover, Poland said that the effectiveness of the vaccine after the first dose was one of the big questions and; that “now we have some information” to take into account.
“Perhaps the best way to protect as many people as possible; … is to give everyone a dose as soon as possible;” Poland said. “I think it is a strategy that should be considered.”
Israel has vaccinated almost half of its population. During the study; a new variant of the virus first identified in the United Kingdom emerged and became the dominant one in Israel; so the results give some clues about the effectiveness of the vaccine against the new variant.
This week two studies carried out in the United Kingdom also revealed good results after a dose of the Pfizer vaccine and also that of AstraZeneca. In Britain the second dose is taking up to 12 weeks to vaccinate as many people as possible.