Video explains how the efficacy of a coronavirus vaccine is measured and why doses cannot be compared

Are some vaccines better than others? How is efficiency measured? Can any of them be 100% effective? Questions about coronavirus vaccines grow in the collective imagination and often lead to doubts or unfounded rejections.

A video published by the international media Vox went viral a few days ago, when it relativizes the difference in effectiveness of each of the vaccines and explains why its application is so important beyond the studies carried out and the percentages disseminated.

The seven-minute video that has already had more than 5.2 million views, takes as trigger the statements of the mayor of Detroit (United States), Mike Duggan, who rejected a shipment of Johnson & Johnson vaccines because their effectiveness was lower than that of Moderna or Pfizer.

“Moderna and Pfizer’s vaccines are the best and I will do everything to ensure that our citizens have the best,” Duggan said at a conference in mid-March.

Indeed, Pfizer’s vaccine was 95% effective and Moderna’s 94% effective, while Johnson & Johnson’s was 66%. but what does that mean?

The video shows that thinking that one vaccine is worse or better than another “is wrong” and explains why.

“The efficacy of the vaccine is estimated in large clinical studies, when tested on thousands of people. These people are divided into two groups. Half receive the vaccine and the other half a placebo. They are then sent to live their lives, while scientists monitor the COVID-19 disease in the following months. In the first Pfizer / BionTech trial, 43,000 people were studied. Ultimately, 170 people got Covid-19. How do these people fit into these two groups? »Begins the explanation.

And he continues, “If we split those 170 people in half, that would mean that even one person could be infected with and without the vaccine, which would be 0% effective. If all 170 had gone to the placebo group and none to the vaccine group, the vaccine would have been 100% effective. With this particular clinical study, there were 162 people in the placebo group and only eight in the vaccinated group, meaning those who received the vaccine had a 95% lower chance of contracting Covid-19. “

“Now that doesn’t mean that if 100 people are vaccinated five of them will get sick. On the contrary, each person vaccinated is 95% less likely to be infected than a person who does not have the vaccine. “

Although the report states that the effectiveness of each vaccine is calculated in the same way, it does make a caveat. It turns out that the studies were conducted at different times and under different circumstances of the pandemic, which could give more or less favorable results. And this is where you explain why it is not practical to compare efficiencies.

For example, Moderna’s trials were conducted entirely in the United States during the summer months, almost at the same time as the Pfizer investigation, at a time when cases were not as large as in winter.

However, Johnson & Johnson conducted their studies between October and January when there was more possibility of contagion. And many other studies have taken place in countries like South Africa and Brazil, as variants of Covid-19 were starting to emerge.

“If we try to make a comparison between each vaccine, they should have been studied in the same clinical trials, with the same inclusion criteria, in the same parts of the world, at the same time,” Amesh Adalja said, Johns Hopkins University Health Security Center specialist.

According to the report, the primary goal of the vaccine is not to prevent infection but to give the body sufficient protection to cover the risks of death, hospitalization and severe symptoms. “In the groups of those who were vaccinated, no one had to be hospitalized or died from Covid-19”he adds. In this, all vaccines were 100% okay.

“The best vaccine for you right now is the one they offer you”concludes Deborah Fuller, member of the Department of Microbiology at the University of Washington.

AFG