Study shows COVID-19 vaccines offer lasting protection
(UNC) - Vaccination offers long-lasting protection from the worst outcomes of COVID-19, according to a new study by the University of North Carolina at Chapel Hill.
The emergence of the delta and omicron variants has raised questions about whether breakthrough infections are caused by waning immunity or by the more transmissible variants.
Results of the study published in the New England Journal of Medicine suggest that declining immunity over time is primarily responsible for breakthrough infections, but vaccines maintained protection from hospitalization and death nine months after getting the first shot.
“The primary takeaway message from our study is that unvaccinated people should get vaccinated right away,” said lead study author Danyu Lin, PhD, Dennis Gillings Distinguished Professor of Biostatistics at the UNC Gillings School of Global Public Health. “The results of our study also underscore the importance of booster shots, especially for older adults.”
The study, which is a collaboration between the UNC-Chapel Hill and the North Carolina Department of Health and Human Services, examined data on COVID-19 vaccination history and health outcomes for 10.6 million North Carolina residents between December 2020 and September 2021.
“We are grateful for the partnership with UNC and for their extensive analysis of N.C. vaccination and case data,” said study author Zack Moore, state epidemiologist and epidemiology section chief at NC DHHS. “This and other recent studies show that vaccination, including boosters, is our best defense against severe illness, hospitalization and death from COVID19. This continues to be true as the virus evolves.”
The study results were used by the Centers for Disease Control and Prevention to support the use of booster shots.
“This is an excellent example of the wonderful research partnership between the Gillings School and NCDHHS, who are working together to generate the evidence base needed to keep our communities safe,” said Penny Gordon-Larsen, PhD, Carla Smith Chamblee Distinguished Professor of Global Nutrition and associate dean for research at UNC Gillings School of Global Public Health
This data included outcomes from COVID-19 cases caused by the delta variant. However, data from this study were collected before the discovery of the omicron variant.
“By applying a novel methodology to the rich surveillance data, we were able to provide precise and comprehensive characterization of the effectiveness over a nine-month period for the three vaccines employed in the U.S.,” Lin said.
“Unlike previous studies, we estimated the vaccine effectiveness in reducing the current risks of COVID-19, hospitalization and death as a function of time elapsed since the first dose,” Lin continued. “This information is critically important in determining the need for and the optimal timing of booster vaccination.”
Immunity remains high months after vaccination
The study found that effectiveness of the Pfizer and Moderna mRNA vaccines in reducing the risk of COVID-19 reached a peak of about 95% at two months after the first dose and then gradually declined. At seven months, the Pfizer vaccine dropped to 67% effectiveness, compared to the Moderna vaccine, which maintained 80% effectiveness.
Among early recipients of the two mRNA vaccines, effectiveness dropped dramatically from mid-June to mid-July, when the delta variant was surging.