Study: COVID-19 Vaccine Prevented Approximately 27 Million Infections in US Adults

Based on a review of the data, investigators observed that the US COVID-19 vaccination program was successful in preventing millions of infections, deaths, and hospitalizations from SARS-CoV-2 in adults in the United States. Specifically, the investigators found that individuals who received a complete vaccine series—either 2 doses of BNT162b2 or mRNA-1273, or 1 dose of JNJ-78436735—was estimated to prevent 30% of all future COVID-19 infections. Vaccination was also found to reduce 33% of all expected hospitalizations and 34% of deaths in individuals aged 18 and older.

“COVID-19 vaccination in the US has provided substantial protection against infections, hospitalizations, and deaths among those who have been vaccinated,” wrote the study authors in their report published in JAMA Network Open. “Vaccination is an effective public health intervention with demonstrable impact, which will be critical in combination with nonpharmaceutical interventions to mitigate the COVID-19 pandemic.”

During the study, investigators aimed to estimate the number of SARS-CoV-2 infections and associated hospitalizations and deaths prevented due to the COVID-19 vaccine in US adults. At the start, the investigators first estimated the burden of COVID-19 by age group, month, and state in the United States using a multiplier model. After gathering data on estimated COVID-19 hospitalizations, the investigators then estimated the number of infections and deaths associated with the virus.

To determine the estimated number of vaccinated individuals in the United States, the investigators used CDC data and calculated the numbers based on age group, month, state, and vaccine type. The results of this analysis indicated that approximately 27 million infections were prevented because of the COVID-19 vaccine. Among those who were fully vaccinated, approximately 235,000 deaths were prevented during the 9-month study period. The vaccine also protected against an even larger 1.6 million hospitalizations in adults aged 18 years and older.

Additionally, the US COVID-19 vaccination program had the greatest impact in terms of averting severe disease in older adults. These age groups not only have the highest rates of hospitalizations and deaths, but they also have the highest rate of vaccine coverage, according to investigators.

The investigating team also observed that the northeast region of the United States likely experienced the most prevention against infections, hospitalizations, and deaths from COVID-19. This estimate was based on the higher rates of vaccination in this population compared to other US regions.

The investigators also noted that the study findings had the limitation of not taking into account reduced infections, hospitalizations, or deaths in unvaccinated people—nor did the findings account for the benefits experienced by partially-vaccinated individuals. Investigators also admitted that they could have underestimated both the burden of severe outcomes in unvaccinated people and accurate hospitalizations caused by COVID-19 infection.

However, investigators did note that the data showed both direct and long-term benefits from a full vaccination. Additionally, the study authors noted that they hope future research will be focused on estimating the impact of vaccination in individuals younger than age 18 years, as well as assess the benefits of partial vaccination, indirect benefits of vaccination on disease transmission, and the impact of additional primary or booster doses.

Reference

Steele M, Couture A, Reed C, et al. Estimated Number of COVID-19 Infections, Hospitalizations, and Deaths Prevented Among Vaccinated Persons in the US, December 2020 to September 2021. JAMA Netw Open. 2022;5(7):e2220385. doi:10.1001/jamanetworkopen.2022.20385