Two studies based on real world data indicate that mRNA COVID-19 vaccines decreased the risk of developing asymptomatic infection.

While one of the studies, from researchers at the Mayo Clinic, was published in a journal, the other was mentioned in a press release. The first study, published in Clinical Infectious Diseases, was a retrospective review of around 48,000 asymptomatic patients in Mayo Clinics in Minnesota, Wisconsin, and Arizona. The patients were subjected to COVID-19 testing before undergoing surgical procedures. This included nearly 3,000 who had been given at least one dose of either the Pfizer or Moderna mRNA vaccine.

About 3.2% of the unvaccinated patients tested positive, compared to 1.4% of those who had been administered a vaccine. After adjustment for confounding variables, the relative risk of asymptomatic infection was 0.35 (95% CI 0.26-0.47) with vaccination. 

In a press release issued on Thursday, Pfizer and BioNTech claimed that their vaccine was 94% effective against asymptomatic SARS-CoV-2 infection. The data came from de-identified aggregate surveillance from the Israeli Ministry of Health between January 17 and March 6… (Medpage Today)