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  • Dr. Drew Park

Pfizer-BioNTech COVID-19 mRNA Vaccine Study Overview

Updated: Jan 2, 2022

Pfizer-BioNTech vaccine phase II/III study overview

Study Population

- 43,448 participants enrolled

- 37,586 participants analyzed for consideration of FDA EUA in Nov 2020

Median follow-up 2 months

Notable Inclusion Criteria:

- Participants ≥ 16 years old

- Participants ≥ 12 years old in later analyses

- Comorbidities in 46.3% of study participants incl obesity (35.1%), diabetes (7.8%) and chronic pulmonary disease (7.8)

- Others include history of HTN, MI, PVD, liver disease, CHF, HBV, HCV and HIV/AIDS

Notable Exclusion Criteria:

- Pregnancy prior or during study period


- Primary Endpoints

(1) Vaccine efficacy after 7 days post Dose 2 in participants without prior evidence of SARS-CoV-2 infection: 95.0%

- 8 COVID-19 cases in vaccinated vs 162 COVID-19 cases in unvaccinated participants

- Similar efficacy across age groups, genders, racial and ethnic groups and participants with medical comorbidities

(2) Vaccine efficacy after 7 days post Dose 2 in participants with or without prior evidence of SARS-CoV-2 infection: 94.6%

- Secondary Endpoints

(1) Prevention of severe COVID-19 following second dose

- 1 severe COVID-19 case in vaccinated vs 3 severe COVID-19 in unvaccinated participants

(2) Prevention of severe COVID-19 following first dose

- Vaccine efficacy: 88.9%

(3) Prevention of COVID-19 following first dose with or without prior evidence of SARS-CoV-2 infection

- Vaccine efficacy: 82.0%


For reference, vaccine efficacy of 50% or greater was considered a successful vaccine at the beginning of development

Cumulative incidence of COVID-19 diverges at ~ Day 14

- Vaccine efficacy for prevention of COVID-19 after first dose 1: 82%.

- But, no data on protection > 21 days after first dose

- Efficacy dose not appear to wane within 2 month study period

Adverse Events:

- Mild to moderate flu-like symptoms 1-2 days after infection representing increased local and systemic immune system activity.

- Most common solicited adverse reactions were injection site reactions (84.1%), fatigue (62.9%), headache (55.1%), muscle pain (38.3%), chills (31.9%), joint pain (23.6%), fever (14.2%).

- Higher incidence after second dose

- Higher incidence in younger study participants

- Proportions of participants who reported at least 1 SAE were 0.6% in the vaccine group and 0.5% in the placebo group.

- Most common SAEs appendicitis (0.04%), acute myocardial infarction (0.02%), cerebrovascular accident (0.02%), pneumonia (0.03%), atrial fibrillation (0.02%), and syncope (0.02%).

- Bell’s palsy reported in greater numbers in the vaccine group but at a rate similar to general population


1. FDA Briefing Document, Pfizer-BioNTech COVID-19 Vaccine, 10 Dec 2020

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