Prevention of the risk of infection, probability of hospitalization or death… As part of a first analysis of its kind, a team compared the effectiveness of two of the most important means of combating Covid-19:the Moderna and Pfizer/BioNtech vaccines. To do this, the researchers relied on the electronic records of American veterans.
Very quickly, the first randomized trials highlighted the strong efficacy of messenger RNA vaccines for the prevention of Covid-19 with an efficacy of 95% for the BNT162b2 (Pfizer-BioNTech) and 94% for mRNA-1273 (Moderna) . Observational studies have subsequently confirmed similar levels of effectiveness in the field. However, so far, direct comparisons of these vaccines have been lacking. So which one is really the most effective?
Both serums focus on the now famous spike protein, but they differ in mRNA content (100g for Moderna versus 30g for Pfizer-BioNTech), and by the interval between the first two doses (four weeks for the first and three weeks for the second). They also differ in the lipid composition of the nanoparticles used to package the mRNA content.
These differences could explain the emerging evidence of a higher antibody response in recipients of the Moderna vaccine. It has also been suggested that this observed difference in antibody levels may translate to a difference in the risk of Covid-19 outcomes. Nevertheless, these analytical works, treated separately, generally involved various groups. So what about when you compare the two vaccines on the same group of people?
As part of this work, the researchers analyzed the cases of American veterans who received the Moderna or Pfizer-BioNTech vaccine from January to May 2021 with 219,842 participants in each group . Note that during this data collection window, the Alpha variant was the dominant strain in circulation.
Published in the New England Journal of Medicine, the study already delivers excellent news. Whether Moderna (mRNA-1273) or Pfizer-BioNTech (BNT162b2), both of these vaccines are still highly effective in the three categories (prevention, hospitalizations and deaths). However, when it came to picking a winner, Moderna came out on top, offering a lower risk of infection and hospitalization against Alpha and Delta strains.
Over 24 weeks of follow-up, the estimated risk of documented infection was indeed 5.75 events per thousand people in the BNT162b2 group and 4.52 events per thousand people in the Moderna group. The documented probability of infection after vaccination was therefore 1.23 additional cases per thousand people in the Pfizer-BioNTech group.
Pfizer-BioNTech also had a slightly higher rate of symptomatic cases (+0.44 per 1000), hospitalizations, ICU admissions (+0.10 per 1000) and deaths (+0.02 per 1000). The differences between the two vaccines are therefore more subtle here.
Despite these few differences, and given their high efficacy, it remains wise to recommend both vaccines equally to anyone with a choice between the two, according to the researchers .
Dr. Barbra A. Dickerman, professor of epidemiology at Harvard and co-author of this work, nevertheless specifies that while these estimated differences in effectiveness are small on an absolute scale, "they can be significant considering the large population scale at which these vaccines are deployed ". Also, "this information may therefore be useful for larger decision-making bodies “.
