Decreased infectivity following BNT162b2 vaccination: A prospective cohort study in Israel
May 18, 2021 |
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 SARSCoV-
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).
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 SARSCoV-
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).
