Reference: N Engl J Med. 2021 Apr 15;384(15):1412-1423
The results of large clinical trials demonstrating efficacy and safety of multiple vaccines targeting SARS-CoV-2 gave us a glimmer of hope at the end of 2020. But it remained uncertain if these vaccines prevented spread, symptoms, and the deadly sequelae of infection outside of clinical trials. Israel kicked off its vaccination campaign in late 2020, setting daily records for rates of vaccination. As of this writing, an estimated 62% of the population is vaccinated.
Investigators conducted a prospective cohort study using data from the largest healthcare organization in Israel. From late December 2020 to February 1, 2021, all newly vaccinated persons receiving Pfizer’s BNT162b2 mRNA vaccine were matched to unvaccinated controls. More than 500,000 persons ≥ 16 years old were included in each group, matched by age, sex, neighborhood, and number of comorbid conditions. Healthcare workers and nursing home residents were excluded because of the high variability in infection risk in these groups. Matched persons had an average age of 45 and more than half had no risk factors for developing severe COVID-19. Each person was followed until the occurrence of a study outcome, non-COVID-19 related death, vaccination of the control, or the end of the study. Mean follow-up time was 15 days and 96% of persons contributing data for ≥ 21 days received the second dose. Vaccine effectiveness was calculated at various time points for all persons with polymerase chain reaction (PCR)-confirmed SARS-CoV-2 and four other outcomes of interest, including symptomatic infection, severe disease, hospitalization, and death due to COVID-19. The estimated vaccine effectiveness ≥ 7 days after the second dose was 92% (95% CI 88%-95%) for documented infection, 94% (95% CI 87%-98%) for prevention of symptomatic disease, and 87% (95% CI 55%-100%) for prevention of hospitalization. Vaccination was estimated to be 46% (95% CI 40%-51%) effective in preventing infection and 72% (95% CI 19%-100%) effective in preventing death due to COVID-19 14-20 days after the first dose. Vaccine effectiveness for the outcome of death could not be calculated ≥ 7 days after the second dose because of a low event rate.
This cohort study conducted in a small country with universal healthcare, a robust public health system, and high rates of vaccine uptake found COVID-19 vaccination to have similar effectiveness to the efficacy initially reported. Within two weeks of the first dose, there appears to be moderate protection against documented infection (although we don’t know much about asymptomatic infection), justifying discussion of prioritization of the first dose. Israel first focused on vaccination of everyone over age 60, which resulted in relatively few older adults with comorbid medical conditions in the study population. At least in this population, trial efficacy has translated into real-world effectiveness. This study should inject more hope into your day as this mRNA vaccine appears to provide robust protection against death from COVID-19.
For more information, see the topic COVID-19 (Novel Coronavirus) in DynaMed.
DynaMed EBM Focus Editorial Team
This EBM Focus was written by Carina Brown, MD, Assistant Professor at Cone Health Family Medicine Residency. Edited by Alan Ehrlich, MD, Executive Editor at DynaMed and Associate Professor in Family Medicine at the University of Massachusetts Medical School, Dan Randall, MD, Deputy Editor for Internal Medicine at DynaMed, and Katharine DeGeorge, MD, MS, Associate Professor of Family Medicine at the University of Virginia and Clinical Editor at DynaMed.