It will have been understood that the study, conducted in full emergence of the delta variant, but before the appearance of Omicron, encourages recall or 3rd dose, but maintains that the vaccines have made it possible to maintain protection against the severe forms, up to 6 to 9 months after the first injection. “The main take-home message is that unvaccinated people should get vaccinated immediately,” insists lead author Danyu Lin, professor of biostatistics at UNC.
The importance of booster shots, especially for the elderly
This is a very broad analysis of COVID-19 vaccination data and health outcomes for 10.6 million North Carolina residents between December 2020 and September 2021. This data included cases of COVID-19 caused by the delta variant but no cases yet associated with the Omicron variant. This analysis specifies the effectiveness of the 3 vaccines (to mRNA Pfizer and Moderna, used in the United States, over a period of 9 months. Specifically, the researchers estimated the effectiveness of the vaccine to reduce the current risks of COVID-19, of hospitalization and death as a function of the time elapsed since the first dose.The objective was to be able to determine the need and the optimal time for a booster.
A decline in the effectiveness of the vaccination after about 6 months
The analysis reveals that:
- the efficacy of the Pfizer and Moderna mRNA vaccines in reducing the risk of COVID-19 peaks at around 95% 2 months after the first dose, then gradually declines;
- at 7 months, the Pfizer vaccine drops to 67% efficacy, the Moderna vaccine maintains an efficacy of 80%;
- in the first people vaccinated with an mRNA vaccine (Pfizer or Moderna), efficacy drops dramatically from mid-June to mid-July, when the delta variant progresses;
- the effectiveness of the Johnson & Johnson vaccine is evaluated at 75% one month after the injection and drops to 60% after 5 months, that is to say well below the 2 mRNA vaccines;
- the 3 vaccines are effective in avoiding hospitalization, including in people with severe COVID-19;
- precisely, the effectiveness of the Pfizer vaccine reaches a peak of 96% at 2 months and then remains stable around 90% up to 7 months; the effectiveness of the Moderna vaccine reaches a peak of 97% at 2 months and then remains stable at 94% up to 7 months. The effectiveness of the Johnson & Johnson vaccine reached a peak of 86% at 2 months and remains above 80% but only until 6 months;
- the 3 vaccines – and it is logical – protect more strongly against death than against hospitalization.
While the majority of vaccines in the United States were administered more than 7 months ago – as in many European countries – and only a small percentage of the population has ever received a booster, the decline in immunity contributes probably to the “revolutionary” wave of infections with the Omicron variant.