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Decreased infectivity following BNT162b2 vaccination: A prospective cohort study in Israel.
Regev-Yochay, Gili; Amit, Sharon; Bergwerk, Moriah; Lipsitch, Marc; Leshem, Eyal; Kahn, Rebecca; Lustig, Yaniv; Cohen, Carmit; Doolman, Ram; Ziv, Arnona; Novikov, Ilya; Rubin, Carmit; Gimpelevich, Irena; Huppert, Amit; Rahav, Galia; Afek, Arnon; Kreiss, Yitshak.
  • Regev-Yochay G; Infection Prevention & Control Unit, Sheba Medical Center, Ramat-Gan, Israel.
  • Amit S; Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel.
  • Bergwerk M; Clinical Microbiology, Sheba Medical Center, Ramat Gan, Israel.
  • Lipsitch M; Infection Prevention & Control Unit, Sheba Medical Center, Ramat-Gan, Israel.
  • Leshem E; Center for Communicable Disease Dynamics, Department of Epidemiology, Harvard Chan School of Public Health, Boston, MA. USA.
  • Kahn R; Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel.
  • Lustig Y; Infecious Disease Unit, Sheba Medical Center, Ramat Gan, Israel.
  • Cohen C; Center for Communicable Disease Dynamics, Department of Epidemiology, Harvard Chan School of Public Health, Boston, MA. USA.
  • Doolman R; Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel.
  • Ziv A; Central Virology Laboratory, Ministry of Health and Sheba Medical Center, Ramat Gan, Israel.
  • Novikov I; Infection Prevention & Control Unit, Sheba Medical Center, Ramat-Gan, Israel.
  • Rubin C; Central laboratory, Sheba Medical Center, Ramat Gan, Israel.
  • Gimpelevich I; Gertner Institute for Epidemiology & Health Policy, Sheba Medical Center, Ramat Gan, Israel.
  • Huppert A; Gertner Institute for Epidemiology & Health Policy, Sheba Medical Center, Ramat Gan, Israel.
  • Rahav G; Infection Prevention & Control Unit, Sheba Medical Center, Ramat-Gan, Israel.
  • Afek A; Gertner Institute for Epidemiology & Health Policy, Sheba Medical Center, Ramat Gan, Israel.
  • Kreiss Y; Gertner Institute for Epidemiology & Health Policy, Sheba Medical Center, Ramat Gan, Israel.
Lancet Reg Health Eur ; 7: 100150, 2021 Aug.
Article in English | MEDLINE | ID: covidwho-1300933
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.

Full text: Available Collection: International databases Database: MEDLINE Type of study: Cohort study / Observational study / Prognostic study Topics: Vaccines Language: English Journal: Lancet Reg Health Eur Year: 2021 Document Type: Article Affiliation country: J.lanepe.2021.100150

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Full text: Available Collection: International databases Database: MEDLINE Type of study: Cohort study / Observational study / Prognostic study Topics: Vaccines Language: English Journal: Lancet Reg Health Eur Year: 2021 Document Type: Article Affiliation country: J.lanepe.2021.100150