Decreased infectivity following BNT162b2 vaccination: A prospective cohort study in Israel

Gili Regev-Yochay; Sharon Amit; Moriah Bergwerk; Marc Lipsitch; Eyal Leshem; Rebecca Kahn; Yaniv Lustig; Carmit Cohen; Ram Doolman; Arnona Ziv; Ilya Novikov; Carmit Rubin; Irena Gimpelevich; Amit Huppert; Galia Rahav; Arnon Afek; Yitshak Kreiss

doi:10.1016/j.lanepe.2021.100150

Decreased infectivity following BNT162b2 vaccination: A prospective cohort study in Israel

Lancet Reg Health Eur. 2021 Aug:7:100150. doi: 10.1016/j.lanepe.2021.100150. Epub 2021 Jul 7.

Authors

Gili Regev-Yochay^{1

2}, Sharon Amit³, Moriah Bergwerk¹, Marc Lipsitch⁴, Eyal Leshem^{2

5}, Rebecca Kahn⁴, Yaniv Lustig^{2

6}, Carmit Cohen¹, Ram Doolman⁷, Arnona Ziv⁸, Ilya Novikov⁸, Carmit Rubin¹, Irena Gimpelevich⁸, Amit Huppert⁸, Galia Rahav⁵, Arnon Afek^{2

9}, Yitshak Kreiss^{2

9}

Affiliations

¹ Infection Prevention & Control Unit, Sheba Medical Center, Ramat-Gan, Israel.
² Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel.
³ Clinical Microbiology, Sheba Medical Center, Ramat Gan, Israel.
⁴ Center for Communicable Disease Dynamics, Department of Epidemiology, Harvard Chan School of Public Health, Boston, MA. USA.
⁵ Infecious Disease Unit, Sheba Medical Center, Ramat Gan, Israel.
⁶ Central Virology Laboratory, Ministry of Health and Sheba Medical Center, Ramat Gan, Israel.
⁷ Central laboratory, Sheba Medical Center, Ramat Gan, Israel.
⁸ Gertner Institute for Epidemiology & Health Policy, Sheba Medical Center, Ramat Gan, Israel.
⁹ General Management, Sheba Medical Center, Ramat Gan, Israel.

Abstract

Background: BNT162b2 was shown to be 92% effective in preventing COVID-19. Prioritizing vaccine rollout, and achievement of herd immunity depend on SARS-CoV-2 transmission reduction. The vaccine's effect on infectivity is thus a critical priority.

Methods: Among all 9650 HCW of a large tertiary medical center in Israel, we calculated the prevalence of positive SARS-CoV-2 qRT-PCR cases with asymptomatic presentation, tested following known or presumed exposure and the infectious subset (N-gene-Ct-value<30) of these. Additionally, infection incidence rates were calculated for symptomatic cases and infectious (Ct<30) cases. Vaccine effectiveness within three months of vaccine rollout was measured as one minus the relative risk or rate ratio, respectively. To further assess infectiousness, we compared the mean Ct-value and the proportion of infections with a positive SARS-CoV-2 antigen test of vaccinated vs. unvaccinated. The correlation between IgG levels within the week before detection and Ct level was assessed.

Findings: Reduced prevalence among fully vaccinated HCW was observed for (i) infections detected due to exposure, with asymptomatic presentation (VE(i)=65.1%, 95%CI 45-79%), (ii) the presumed infectious (Ct<30) subset of these (VE(ii)=69.6%, 95%CI 43-84%) (iii) never-symptomatic infections (VE(iii)=72.3%, 95%CI 48-86%), and (iv) the presumed infectious (Ct<30) subset (VE(iv)=83.0%, 95%CI 51-94%).Incidence of (v) symptomatic and (vi) symptomatic-infectious cases was significantly lower among fully vaccinated vs. unvaccinated individuals (VE(v)= 89.7%, 95%CI 84-94%, VE(vi)=88.1%, 95%CI 80-95%).The mean Ct-value was significantly higher in vaccinated vs. unvaccinated (27.3±1.2 vs. 22.2±1.0, p<0.001) and the proportion of positive SARS-CoV-2 antigen tests was also significantly lower among vaccinated vs. unvaccinated PCR-positive HCW (80% vs. 31%, p<0.001). Lower infectivity was correlated with higher IgG concentrations (R=0.36, p=0.01).

Interpretation: These results suggest that BNT162b2 is moderately to highly effective in reducing infectivity, via preventing infection and through reducing viral shedding.

Funding: Sheba Medical Center, Israel.

Abstract

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