COVID-19 mRNA Vaccines Show High Effectiveness Among Healthcare Workers

By Amy Orciari Herman

Edited by David G. Fairchild, MD, MPH, and Lorenzo Di Francesco, MD, FACP, FHM

Several correspondences published in the New England Journal of Medicine add to evidence on the effectiveness of the COVID-19 mRNA vaccines in healthcare settings.

In the first, researchers examined post-vaccination SARS-CoV-2 infection among nearly 37,000 healthcare workers from two California health systems who received at least one dose of mRNA vaccine between December 2020 and February 2021; three fourths also received their second dose. Regular PCR testing of asymptomatic workers was mandatory in one of the health systems and optional in the other. Overall, 379 people (1%) tested positive after vaccination, 71% of whom did so in the first 2 weeks after the first dose. Just eight workers tested positive 8 to 14 days after the second dose, and seven did so 15 or more days after the second dose. The researchers write, "The rarity of positive test results 14 days after administration of the second dose of vaccine is encouraging and suggests that the efficacy of these vaccines is maintained outside the trial setting." They add that the findings "underscore the critical importance of continued public health mitigation measures ... even in environments with a high incidence of vaccination."

Next, researchers studied roughly 23,000 employees at a Texas medical center who received at least one dose of mRNA vaccine between December and January, 30% of whom also received their second dose. By the end of January, 1.8% of partially vaccinated workers and 0.05% of fully vaccinated workers tested positive for SARS-CoV-2 — versus 2.6% of unvaccinated employees. The researchers note that the number of positive tests among all workers was lower than the number projected based on increasing positivity among emergency department patients during the period. They call the effect of vaccination on the center's workforce "dramatic," observing more than a 90% reduction in the number of workers in isolation or quarantine.

Finally, a study among some 5300 vaccinated healthcare workers from a Jerusalem medical system corroborates the Pfizer-BioNTech vaccine's real-world effectiveness. In this group, the number of vaccinated workers who tested positive for SARS-CoV-2 declined beginning the third week after the first dose. During the seventh week of follow-up, just four vaccinated workers who'd received their second dose tested positive. The authors note that the community had a high incidence of COVID-19 during this period.