The U.S. COVID-19 vaccination program prevented millions of infections as well as hundreds of thousands of deaths, according to a modeling study.
From December 2020 through September 2021, COVID-19 vaccines were estimated to have prevented about 27 million infections, 1.6 million hospitalizations, and 235,000 deaths among U.S. adults, reported Molly K. Steele, PhD, MSc, MPH, of the CDC, and colleagues.
During the month of September 2021 alone, vaccines were estimated to have prevented 52% of expected infections, 56% of expected hospitalizations, and 58% of expected deaths in adults, the authors noted 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,” they concluded.
Most of the hospitalizations and deaths prevented occurred in adults 65 and older, with 759,000 hospitalizations and 154,000 deaths prevented. The 50-64 age group followed closely behind, with 525,000 hospitalizations and 66,000 deaths prevented.
“This study is among the first, to our knowledge, to present estimates of age group-specific impacts of vaccination among vaccinated persons in the U.S. over time and by HHS region,” Steele and team wrote.
“Our estimates, particularly in the early part of 2021, are relatively conservative because most vaccinated individuals during this period were older adults (i.e., older adults were prioritized for vaccination early compared with younger adults); we also included lower VE [vaccine effectiveness] estimates for those 65 years or older,” they noted.
“The piecemeal nature of COVID-19 data highlights an urgent need to develop a comprehensive national data collection infrastructure. Nationally representative data on infections, hospitalizations, deaths, and vaccination are needed to prepare for the next pandemic,” pointed out Westyn Branch-Elliman, MD, MMSc, of the section of infectious diseases at the VA Boston Healthcare System, and colleagues in an invited commentary.
For this study, a multiplier model was used to extrapolate the number of infections and COVID-associated deaths from data on the number of COVID-associated hospitalizations broken down by state, month, and age group (18-49, 50-64, and 65 and older) from December 2020 through September 2021, factoring in the official start of the U.S. vaccination program on Dec. 12, 2020, as well as subsequent staggered rollouts.
The approximate numbers of those who had completed vaccination were taken from state-reported CDC data, as well as from the Vaccine Administration Management System.
By the end of September 2021, approximately 67% of those 18 and older and 83% of those 65 and older had received either two doses of the Moderna or Pfizer-BioNTech mRNA vaccines, or one dose of the Johnson & Johnson vaccine.
Unsurprisingly, while those in the 18-49 age group saw the highest cumulative number of infections, at 29,000 per 100,000 population, those in the 65 and older age group saw the highest cumulative number of hospitalizations and deaths, at 2,740 and 560 per 100,000 population, respectively.
Using previous research that had estimated 3.36 million hospitalizations from COVID-19 during the 10-month time frame, Steele and team estimated that 69 million infections and 431,000 deaths occurred as a result of COVID-19 during this time.
The authors acknowledged that there are many limitations to the study, as the models could not factor in vaccine-induced reductions in transmission, partial vaccination, acquired immunity from previous infections, or waning immunity.
“Future models and analyses could estimate the impact of vaccination among individuals younger than 18 years, the benefits of partial vaccination, indirect benefits of vaccination on disease transmission, and the impact of additional primary or booster doses,” they wrote.
This study was funded by the CDC.
The study authors reported no conflicts of interest.
Two of the commentators reported receiving grants from the CDC and the U.S. Department of Veterans Affairs outside the submitted work, as well as institutional grants from Gilead Sciences outside the submitted work.