New research has found that COVID vaccination offers long-lasting protection from the worst outcomes of infection. The research has been published in the 'New England Journal of Medicine'. The emergence of the Delta and Omicron variants had raised questions about whether breakthrough infections are caused by waning immunity or by the more transmissible variants. Results of the study suggested 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 of our study also underscore the importance of booster shots, especially for older adults," Lin added.
"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," Lin added.
The study found that the effectiveness of the Pfizer and Moderna mRNA vaccines in reducing the risk of COVID-19 reached a peak of about 95 per cent two months after the first dose and then gradually declined. At seven months, the Pfizer vaccine dropped to 67 per cent effectiveness, compared to the Moderna vaccine, which maintained 80 per cent 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 per cent at one month after injection and fell to 60 per cent 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 per cent at two months and remained around 90 per cent at seven months; effectiveness of the Moderna vaccine reached a peak of 97 per cent at two months and remained at 94 per cent at seven months. The effectiveness of the Johnson & Johnson vaccine reached a peak of 86 per cent at two months and was higher than 80 per cent through six months. For all three vaccines, effectiveness against death was higher than that of hospitalization.
"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," Lin said.
Meanwhile, everyone age 5 and older are eligible for a COVID-19 vaccine. Those ages 18 and up should get a booster shot.