In a new study from the University of North Carolina at Chapel Hill, researchers found vaccination offers long-lasting protection from the worst outcomes of COVID-19.
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.
The team suggests that declining immunity is responsible for breakthrough infections, but vaccines maintained protection from hospitalization and severe disease nine months after getting the first shot.
In the study, the team examined data on COVID-19 vaccination history and health outcomes for 10.6 million North Carolina residents between December 2020 and September 2021.
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.
The team found that the 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.
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 due to 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.
The 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 hospitalization.
The team says because the majority of the vaccines in the U.S. were administered more than seven months ago and only a small percentage of the population has received boosters, waning immunity is likely contributing to the breakthrough infections with the omicron variant.
Everyone age 5 and older is eligible for a COVID-19 vaccine. Those ages 18 and up should get a booster shot.
If you care about Covid, please read studies that weight loss may help prevent severe COVID-19, and it is better to get COVID vaccination in afternoon.
For more information about health, please see recent studies about Pfizer vaccination that provides 70% protection from Omicron, and results showing that people infected with Omicron less likely to get Delta infection.
The study is published in the New England Journal of Medicine. One author of the study is Danyu Lin, Ph.D.
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