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The coronavirus vaccine developed by Pfizer and BioNTech offers very high protection against symptomatic illness, serious illness and death, coming close to the level of protection announced by the companies in their Phase III clinical trial. This is the clear conclusion of the most in-depth and comprehensive study published to date.
It is based on medical data from 1.2 million patients belonging to the Israeli health-maintenance organization Clalit Health Services – half of whom were vaccinated and the other half were not.
Three months after the real-world coronavirus vaccinations began and two months after the Israeli campaign began in late December, the safety of the vaccine is crystal clear, as tens of millions of people have received it without worrying side effects. But until now, the question of whether it was really as effective against the coronavirus as clinical trials have shown has remained unanswered.
Israel was not the first country to start vaccinations. But the pace and scale of its vaccination campaign, combined with the wealth of medical data from its HMOs and stored in a few central databases, made it a global test of the vaccine’s effectiveness.
Therefore, all efficacy studies published in the past two months have relied on Israeli data. They have used a variety of methods to examine the effectiveness of the vaccine, and most have yet to be peer reviewed.
The latest study, published Thursday in a leading journal, the New England Journal of Medicine, was conducted by researchers at the Clalit Research Institute. He used the most precise statistical methods available to analyze real-world data to come as close as possible to the gold standard of clinical research.
The authors are Prof. Ran Balicer, Dr Noa Dagan, Dr Noam Barda, Dr Eldad Kepten, Oren Miron, Shay Perchik and Prof. Mark Katz de Clalit, in addition to three senior researchers in the field from Harvard University – Miguel Hernan, Marc Lipsitch and Ben Reis.
The study found that the vaccine prevented 94 percent of cases of symptomatic illness on average; the full range is 87 to 98 percent. Given that the study involved 1.2 million people, compared to only around 40,000 in the Phase III clinical trial, it also provides a clear answer to the question of the vaccine’s effectiveness in preventing cases of severe disease. – 92%.
According to analyzes done by the Clalit Research Institute based on updated data from the HMO, after writing the article, they found that those vaccinated are 86-98% less likely to become seriously ill from one week after the second dose. But the study also found that the vaccine begins to work even two weeks after the first dose, preventing 57% of cases of symptomatic infection and producing a 62% drop in the number of critically ill patients.
The large number of people participating in the study also allowed researchers to determine the number of deaths prevented by the vaccine. He found that on the 27th day, the level of protection against death reached 84%.
The latest unpublished data shows the vaccine prevents 85-100% of deaths. In short, “during each of the periods of time the protection against death equals or exceeds the protection against serious illness”.
Finally, the vaccine prevented 92% of documented cases of infection. This is not the same as the number of total infections it prevents, because to determine this it would be necessary to test people at random for asymptomatic carriers. Clalit now does precisely that and will publish the results later.
The biggest difference between the first and second dose is in this statistic: up to a week after the second dose, the vaccine is only 60% effective in preventing documented infections, but after that it switches to 92%.
Clalit’s research shows the vaccine to be extremely effective, but slightly less than claimed by other studies published in recent weeks, including studies from the Israeli Ministry of Health. The problem with previous studies was that they did not take into account the significant differences between population groups that were more or less likely to be vaccinated. These differences, mainly socio-economic, affect both their likelihood of contracting the virus and the likelihood of having pre-existing conditions that exacerbate it.
The fundamental problem with reaching conclusions about the actual effectiveness of a vaccine, even with data from hundreds of thousands of people to rely on, is that no actual study can meet the basic requirements of clinical trials.
First, in the real world, the division between the research group and the control group – that is, the unvaccinated – is neither random nor controlled. There can be many differences between people who get vaccinated and those who don’t, and researchers can’t control who belongs to which group.
Second, in the real world, people who have been vaccinated know they are getting the vaccine. Clinical trials are double-blind, which means neither the researchers nor the subjects know who got the vaccine and who got a placebo – to avoid any possibility that this knowledge could skew the results. In real life, knowing that they have been vaccinated can change people’s behavior, thereby changing their risk of infection unrelated to the biological impact of the vaccine.
To compensate for these problems, Clalit researchers used sophisticated statistical tools to make their research and control groups as similar as possible. For each of the 600,000 people vaccinated, they found in their databases an unvaccinated “twin” whose demographic, health and socio-economic characteristics were as similar as possible.
And twins aren’t just similar in age and gender. For example, if there’s a 56-year-old ultra-Orthodox vaccinated man who lives in a specific area of Tel Aviv, who has two underlying illnesses and was vaccinated against the flu last year, researches the ” pair up ”with an ultra-Orthodox 56-year-old man who lives in the same area, who has the same two underlying illnesses and was vaccinated against the flu last year – but has not been vaccinated against the coronavirus.
Tracking viral statistics among these two groups allows researchers to accurately measure vaccine effectiveness while controlling for most other factors that may influence the results.
Critical and clear evidence
The bottom line is that the Clalit study provides critical and clear scientific evidence for the efficacy of vaccines, but the study also clearly shows that protection is not complete and therefore we must continue to conduct ourselves in a calculated manner. and careful with those most at risk of serious disease, even if they are vaccinated.
Given this, will vaccines ever allow us to say goodbye to the coronavirus, and if so, when? What percentage of the population needs to be vaccinated to create collective immunity that will prevent the virus from spreading?
To answer this, we need to know how well the vaccine actually prevents people from getting infected (and therefore infecting others as well). It is hoped that studies like the one Clalit is currently working on will help answer this question, giving us a better understanding of what we need to do to truly beat the virus.
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