In one report, just 0.4 percent of healthcare workers in Israel who received both shots of the COVID-19 immunization later tested positive compared to 7.2 percent of unvaccinated employees.
This means healthcare workers who received both doses were 18 times less likely to fall ill.
Meanwhile, in the second study, 1.8 percent of fully vaccinated frontline staff at a hospital in Tennessee contracted the virus in comparison with 8.5 percent of unvaccinated workers, putting the latter group at a 4.7 times greater risk of infection.
The results are in line with the 95 percent efficacy Pfizer and BioNTech reported from their late-stage clinical trial in December 2020 that led to emergency use authorization from the Food and Drug Administration (FDA).
At a hospital in Tel Aviv, Israel, 5,517 healthcare workers, or 82.2% (light blue line), received two doses between December and February and 757, 11.3% (yellow line) were not vaccinated. Of them, 0.4% of the fully vaccinated later tested positive for Covid compared to 7.2% of unvaccinated people
In a second study at a hospital in Tennessee, 2,776 employees, 53.2%, were fully vaccinated 2,165 staff members, 41.5%, were unvaccinated. Of those, 1.8% of the fully vaccinated later tested positive for Covid (yellow line) compared to 8.5% of the unvaccinated workers (blue line)
For the study, published in the Journal of the American Medical Association (JAMA), the team from the Tel Aviv Sourasky Medical Center collected data from 6,710 of their employees.
Between December 20, 2020, and February 25, 2021, 5,953, or 88.7 percent, received at least one dose and 5,517, or 82.2 percent, received two doses.
The remaining 757, 11.3 percent, were not vaccinated.
Workers were considered fully vaccinated once it was seven days or later after receiving their final dose.
Of the fully vaccinated employees, 27 of the 5,517, or 0.4 percent, later tested positive for the virus, as did 55 of the 757, or 7.2 percent, of the unvaccinated staff.
In the Israel study, just 8 fully vaccinated people (solid blue line) were symptomatic and 19 were asymptomatic (dotted blue line) compared to 38 symptomatic unvaccinated workers (solid yellow line) and 17 asymptomatic workers (dotted yellow line)