In a recent study published in the New England Journal of Medicine, researchers found vaccination offers long-lasting protection from the worst outcomes of COVID-19.
The study is from the University of North Carolina at Chapel Hill and was conducted by Danyu Lin, et al.
The delta and omicron variants have 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% 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.
The effectiveness of the Johnson & Johnson adenovirus vaccine was 75% 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.
The effectiveness of the Pfizer vaccine reached a peak of 96% at two months and remained around 90% at seven months; the 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 are eligible for a COVID-19 vaccine. Those ages 18 and up should get a booster shot.
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