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 2nd 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 1st dose
- 6037 (66%) had received a 2nd 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 1st dose
- 3 (2%) tested positive after the 2nd dose
-
All SARS-CoV-2 Positive Rate in Vaccinated vs Unvaccinated:
- Unvaccinated: 7.4/10,000 person-days
-
1 – 14 days after 1st 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 1st 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 1st 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 1st Dose: 1.2/10,000 person-days
- Adjusted Rate Reductions of SARS-CoV-2 Infections Compared to Unvaccinated = 85% (95% CI 71 to 92)
- 170 SARS-CoV-2 infections of which 99 (58%) were symptomatic with COVID-19
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:
- Amit S et al. Early Rate Reductions of SARS-CoV-2 Infection and COVID-19 in BNT162b2 Vaccine Recipients. Lancet 2021.
Post Peer Reviewed By: Anand Swaminathan, MD (Twitter: @EMSwami)
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