“This is the first peer-reviewed evidence of a vaccine's effectiveness under real world conditions,” said Ben Reis, one of the co-authors of this study published Wednesday in the prestigious New England Journal of Medicine.
So far, the efficacy of the vaccine has been proven by clinical trials carried out on thousands of people, but not under real conditions, which involve a greater variety of people and behaviors or even logistical challenges such as maintaining the cold chain.
The study was conducted using data from some 1.2 million people treated by one of Israel's largest health organizations (Clalit Health Services), between December 20, 2020 and February 1, 2021. A By this time, the British variant was circulating widely in the country, making these results all the more interesting.
Almost 600,000 people who received the vaccine were “associated” very rigorously with some 600,000 others who did not receive the injection, and who had very similar characteristics in terms of sex, age, but also comorbidities and place of residence.
By comparing the two groups, the authors show that vaccination reduced symptomatic cases of Covid-19 by 94%, severe cases of the disease by 92%, and hospitalizations by 87%.
These rates apply to the protection obtained at least seven days after the second injection.
But "a fairly significant effect was observed even before the second dose", noted with AFP Noam Barda, one of the two main authors, with an effectiveness of 57% for cases of Covid-19 with symptoms, and 62% for severe cases.
Effective against infection?
The vaccine was also 72% effective in preventing deaths from Covid-19 after the first dose, but their low number in this study makes this result less reliable.
Effectiveness was relatively consistent for all age groups, "including people over 70," said Ben Reis.
On the other hand, “we have indications that for people with a lot of (past) illnesses, the vaccine works slightly less well.
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In addition, the study reports a 92% effectiveness against the very possibility of being infected (and not only of developing symptoms).
This is crucial data, because if confirmed, it could indicate that vaccinated people can no longer transmit the virus.
But this result must be taken with caution, by the authors' own admission.
It is encouraging but at the same time "this study cannot guarantee that we have detected all asymptomatic infections", warned Noam Barda.
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For that, it would be necessary that all the participants are tested very regularly, in a proactive way, which was not the case here.
Another study by Clalit in this direction is in progress.