All three COVID-19 vaccines had durable effectiveness in reducing the risks of hospitalisation and death, found a US analysis of 10.6m people.
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 with 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.
Effectiveness for the Johnson & Johnson adenovirus vaccine was 75% at one month after injection and fell to 60% after five months.
All three vaccines were effective at keeping people out of the hospital with severe COVID-19. Effectiveness of the Pfizer vaccine reached a peak of 96% at two months and remained around 90% at seven months; effectiveness of the Moderna vaccine reached a peak of 97% at two months and remained at 94% at seven months.
Effectiveness of the Johnson & Johnson vaccine reached a peak of 86% at two months and was higher than 80% through six months.
For all three vaccines, effectiveness against death was higher than that of hospitalisation.
Results of the study, University of North Carolina at Chapel Hill, published in the New England Journal of Medicine, suggest that declining immunity is responsible for breakthrough infections, but vaccines maintained protection from hospitalisation and severe disease 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 also underscore the importance of booster shots, especially for older adults.”
The study, 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 10.6m North Carolina residents between December 2020 and September 2021.
The results were used by the US Centers for Disease Control and Prevention (CDC) to support the use of booster shots.
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, said that the 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 characterisation of the effectiveness over a nine-month period for the three vaccines employed in the US,” Lin said.
“Unlike previous studies, we estimated the vaccine effectiveness in reducing the current risks of COVID-19, hospitalisation and death as a function of time elapsed since the first dose. This information is critically important in determining the need for and the optimal timing of booster vaccination.”
“Because the majority of the vaccines in the US were administered more than seven months ago and only a small percentage of the population has received boosters, waning immunity may be contributing to the breakthrough infections with the Omicron variant,” Lin said.
Study details
Effectiveness of Covid-19 Vaccines over a 9-Month Period in North Carolina.
Dan-Yu Lin, Yu Gu, Bradford Wheeler, Hayley Young, Shannon Holloway, Shadia-Khan Sunny, Zack Moore, Donglin Zeng.
Published in the New England Journal of Medicine on 12 January 2022
Abstract
Background
The duration of protection afforded by coronavirus disease 2019 (COVID-19) vaccines in the United States is unclear. Whether the increase in post-vaccination infections during the summer of 2021 was caused by declining immunity over time, the emergence of the B.1.617.2 (Delta) variant, or both is unknown.
Methods
We extracted data regarding COVID-19–related vaccination and outcomes during a 9-month period (December 11, 2020, to September 8, 2021) for approximately 10.6 million North Carolina residents by linking data from the North Carolina COVID-19 Surveillance System and the COVID-19 Vaccine Management System. We used a Cox regression model to estimate the effectiveness of the BNT162b2 (Pfizer–BioNTech), mRNA-1273 (Moderna), and Ad26.COV2.S (Johnson & Johnson–Janssen) vaccines in reducing the current risks of COVID-19, hospitalisation, and death, as a function of time elapsed since vaccination.
Results
For the two-dose regimens of messenger RNA (mRNA) vaccines BNT162b2 (30 μg per dose) and mRNA-1273 (100 μg per dose), vaccine effectiveness against COVID-19 was 94.5% (95% confidence interval [CI], 94.1 to 94.9) and 95.9% (95% CI, 95.5 to 96.2), respectively, at 2 months after the first dose and decreased to 66.6% (95% CI, 65.2 to 67.8) and 80.3% (95% CI, 79.3 to 81.2), respectively, at 7 months. Among early recipients of BNT162b2 and mRNA-1273, effectiveness decreased by approximately 15 and 10 percentage points, respectively, from mid-June to mid-July, when the delta variant became dominant. For the one-dose regimen of Ad26.COV2.S (5×1010 viral particles), effectiveness against COVID-19 was 74.8% (95% CI, 72.5 to 76.9) at 1 month and decreased to 59.4% (95% CI, 57.2 to 61.5) at 5 months. All three vaccines maintained better effectiveness in preventing hospitalisation and death than in preventing infection over time, although the two mRNA vaccines provided higher levels of protection than Ad26.COV2.S.
Conclusions
All three COVID-19 vaccines had durable effectiveness in reducing the risks of hospitalisation and death. Waning protection against infection over time was due to both declining immunity and the emergence of the Delta variant.
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