Data from Israel in Health-Care Workers Vaccinated with 1st Dose of the Pfizer COVID-19 Vaccine

Background: Israel has succeeded in ramping up its vaccination program faster than any nation in the world. In December 2020, Israel began a national immunization campaign prioritizing health-care workers. In the original clinical trial data, the Pfizer vaccine was estimated to prevent 52.4% of COVID-19 before dose two and 90.5% on days 2 – 7 after dose two. However, it is important to study the effectiveness of the vaccines in a real world setting.

Paper: Amit S et al. Early Rate Reductions of SARS-CoV-2 Infection and COVID-19 in BNT162b2 Vaccine Recipients. Lancet 2021. PMID: 33610193 

Clinical Question: How effective is the Pfizer COVID-19 vaccine in decreasing viral transmission in health care workers with a single injection (i.e. prior to 14d post 2^nd injection) of the Pfizer mRNA COVID-19 vaccine?

What They Did:

• Analyzed a retrospective cohort of 9,109 vaccine-eligible health-care workers
• Examined early reductions in SARS-Co-V-2 infection and COVID-19 rates in vaccinated health-care workers vs unvaccinated health care workers

Outcomes:

• Positive SARS-CoV-2 PCR Infection
• Symptomatic COVID-19

Inclusion:

• All health-care workers

Exclusion:

• Previous SARS-CoV-2 infection

Results:              

• By Jan 24, 2021 of the 9,109 eligible staff:
  • 7,214 (79%) had received a 1^st dose
  • 6037 (66%) had received a 2^nd dose
• Overall:
  • 170 SARS-CoV-2 infections of which 99 (58%) were symptomatic with COVID-19
    • 89 (52%) were unvaccinated
    • 78 (46%) were positive after the 1^st dose
    • 3 (2%) tested positive after the 2^nd dose
  • All SARS-CoV-2 Positive Rate in Vaccinated vs Unvaccinated:
    • Unvaccinated: 7.4/10,000 person-days
    • 1 – 14 days after 1^st Dose: 5.5/10,000 person-days
      • Adjusted Rate Reductions of SARS-CoV-2 Infections Compared to Unvaccinated = 30% (95% CI 2 to 50)
    • 15 – 28 days after 1^st Dose: 3.0/10,000 person-days
      • Adjusted Rate Reductions of SARS-CoV-2 Infections Compared to Unvaccinated = 75% (95% CI 72 to 84)
  • Symptomatic COVID-19 Rate in Vaccinated vs Unvaccinated:
    • Unvaccinated: 5.0/10,000 person-days
    • 1 – 14 days after 1^st Dose: 2.8/10,000 person-days
      • Adjusted Rate Reductions of SARS-CoV-2 Infections Compared to Unvaccinated = 47% (95% CI 17 to 66)
    • 15 – 28 days after 1^st Dose: 1.2/10,000 person-days
      • Adjusted Rate Reductions of SARS-CoV-2 Infections Compared to Unvaccinated = 85% (95% CI 71 to 92)

Clinical Take Home Point: This data from Israel on health-care workers that were vaccinated with the COVID-19 Pfizer vaccine shows a significant reduction in SARS-CoV-2 infection (asymptomatic) and symptomatic COVID-19 rates following the first vaccine dose, especially after the 15 to 28d post vaccination mark.

References:

1. Amit S et al. Early Rate Reductions of SARS-CoV-2 Infection and COVID-19 in BNT162b2 Vaccine Recipients. Lancet 2021.
   PMID: 33610193

Post Peer Reviewed By: Anand Swaminathan, MD (Twitter: @EMSwami)