By Jeanie Quach

As vaccines roll out, studies are underway to continue to monitor their efficacy against SARS-CoV-2 infection, and particularly, against asymptomatic infections. Two recent publications in JAMA show that vaccination with the Pfizer-BioNTech vaccine reduces the risk of any SARS-CoV-2 infection, whether with symptoms or not.

 

Main Conclusions:

  • Vaccination with the Pfizer-BioNTech vaccine in healthcare and hospital workers reduced the risk of symptomatic and asymptomatic infections with SARS-CoV-2.

 

Although there are associations between vaccination and a reduction in symptomatic disease with the clinical trials, it is unclear if there is an association between vaccination and asymptomatic infections or transmission. A study conducted at the St. Jude Children’s Research hospital in the U.S. recruited 5217 vaccinated and unvaccinated healthcare workers. Among the vaccinated employees, 51 tested positive (1.7%) for SARS-CoV-2 during follow-ups (median of 72 days). Of these positive cases, 29 (56.9%) were diagnosed as asymptomatic infections. Among unvaccinated employees, 185 tested positive (8.5%) for SARS-CoV-2 during follow-up (median of 81 days) and 79 (42.7%) individuals in this cohort were asymptomatic.

Based on these results, vaccinated individuals had an approximately 1.0% risk of getting an asymptomatic infection, and unvaccinated individuals had a 3.6% of getting an asymptomatic infection. Altogether, these results indicate that hospital employees vaccinated with the Pfizer-BioNTech vaccine have a decreased risk of both symptomatic and asymptomatic infections with SARS-CoV-2. Finally, the authors highlighted that further research with a longer follow-up time and a larger cohort size is needed to strengthen their observations.

Tang L, Hijano DR, Gaur AH, Geiger TL, Neufeld EJ, Hoffman JM, Hayden RT. Asymptomatic and symptomatic SARS-CoV-2 Infections after BNT162b2 vaccination in a routinely screened workforce. JAMA. 2021 May 6. doi: 10.1001/jama.2021.6564.

 

Another study conducted on healthcare workers at a medical center in Tel Aviv, Israel, with 6710 participants, included those that had received either one or two doses of the Pfizer-BioNTech vaccine, or were not vaccinated. The authors wanted to determine the incidence of SARS-CoV-2 infection in vaccinated versus unvaccinated healthcare workers during a median follow-up of 63 days.

Symptomatic SARS-CoV-2 infections occurred in eight fully vaccinated healthcare workers, while 38 infections were detected in the unvaccinated group. The incidence rate of symptomatic SARS-CoV-2 infection was calculated to be 4.7 per 100 000 person-days in the fully vaccinated cohort vs 149.8 per 100 000 person-days in the unvaccinated cohort. Asymptomatic SARS-CoV-2 infection occurred in 19 fully vaccinated healthcare workers and 17 unvaccinated workers. The incidence rate of asymptomatic SARS-CoV-2 infection was calculated to be 11.3 per 100 000 person-days in the fully vaccinated cohort vs 67.0 per 100 000 person-days in the unvaccinated cohort.

Similar to the U.S. study mentioned above, healthcare workers who have been vaccinated with the Pfizer-BioNTech vaccine were associated with a significantly lower incidence of both symptomatic and asymptomatic SARS-CoV-2 infection. Yet, both studies ultimately wanted to determine whether a reduction in risk of asymptomatic infection is associated with reduced transmission.

Angel Y, Spitzer A, Henig O, Saiag E, Sprecher E, Padova H, Ben-Ami R. Association between vaccination with BNT162b2 and incidence of symptomatic and asymptomatic SARS-CoV-2 infections among health care workers. JAMA. 2021 May 6. doi: 10.1001/jama.2021.7152.