Fourth dose of Pfizer vaccine may provide additional protection to elderly against severe disease: NEJM

The results of this study stated as follow:

1. The aggregated four-dose groups had 1.5 cases of severe Covid-19 per 100,000 person-days (unadjusted rate), 4.2 in the internal control group and 3.9 in the three-dose group.

2. In the quasi-Poisson analysis, the adjusted rate of severe Covid-19 in the fourth week after receiving the fourth dosage was 3.5 times lower than in the three-dose group and 2.3 times lower than in the internal control group.

3. During the six weeks following the fourth dose, there was no deterioration in protection against severe sickness.

4. The aggregated four-dose groups had 177 instances of proven infection per 100,000 person-days, 361 in the three-dose group, and 388 in the internal control group.

5. The adjusted rate of confirmed infection in the quasi-Poisson analysis of the fourth week after receiving the fourth dosage was lower by a factor of 2.0 than in the three-dose group and by a factor of 1.8 than in the internal control group.

6. This protection, however, began to decrease in the following weeks.

In conclusion, these results demonstrated the efficacy of a fourth vaccination dosage against severe disease caused by the omicron variant, when compared to a third dose delivered more than 4 months earlier. A fourth dosage found to give only short-term protection and a minor absolute advantage in cases of confirmed infection.

Reference:

Bar-On, Y. M., Goldberg, Y., Mandel, M., Bodenheimer, O., Amir, O., Freedman, L., Alroy-Preis, S., Ash, N., Huppert, A., & Milo, R. (2022). Protection by a Fourth Dose of BNT162b2 against Omicron in Israel. In New England Journal of Medicine. Massachusetts Medical Society. https://doi.org/10.1056/nejmoa2201570