A recent study utilized surveillance data to evaluate the long-term effectiveness of Pfizer, Moderna, and Johnson & Johnson COVID-19 vaccines in preventing SARS-CoV-2 infection, hospitalizations, and deaths. This large study found that the three vaccines, especially the Pfizer and Moderna mRNA vaccines, provided a high degree of protection against severe illness at least 6 months after vaccination.

In a recent publication in the NEJM, researchers evaluated the long-term effectiveness of these vaccines. The researchers obtained linking data from the North Carolina COVID-19 Surveillance System and the COVID-19 Vaccine Management System regarding COVID-19–related vaccination and outcomes during a 9-month period (December 11, 2020 to September 8, 2021) for an estimated 10.6 million North Carolina residents.

Researchers utilized a Cox regression model to estimate the effectiveness of the BNT162b2 (Pfizer–BioNTech), mRNA-1273 (Moderna), and Ad26.COV2.S (Johnson & Johnson–Janssen) vaccines in decreasing the current risks of COVID-19, hospitalization, and death as a function of time elapsed since vaccination. The objective of this study was to characterize further the durability of protection provided by the three FDA-approved COVID-19 vaccines.

Results showed that for the two-dose regimens of messenger RNA (mRNA) vaccines BNT162b2 (30 mcg per dose) and mRNA-1273 (100 mcg per dose), vaccine effectiveness against COVID-19 was 94.5% (95% CI, 94.1-94.9) and 95.9% (95% CI, 95.5-96.2), respectively, at 2 months after the first dose and decreased to 66.6% (95% CI, 65.2-67.8) and 80.3% (95% CI, 79.3-81.2), respectively, at 7 months. Among early recipients of BNT162b2 and mRNA-1273, effectiveness decreased by approximately 15 and 10 percentage points, respectively, from mid-June to mid-July, when the Delta variant became dominant.

For the one-dose regimen of Ad26.COV2.S (5x1010 viral particles), effectiveness against COVID-19 was 74.8% (95% CI, 72.5-76.9) at 1 month and decreased to 59.4% (95% CI, 57.2-61.5) at 5 months. All three vaccines maintained better effectiveness in preventing hospitalization and death than in preventing infection over time, although the two mRNA vaccines provided higher levels of protection than that of Ad26.COV2.S.

The authors concluded that all three COVID-19 vaccines had durable effectiveness in decreasing the risks of hospitalization and death. They also noted that waning protection against infection over time was due to both dwindling immunity and the emergence of the Delta variant.

In an interview on the Medical News Today website, lead author of the study, Dr. Dan-Yu Lin, a professor at the University of North Carolina at Chapel Hill, stated, "Many decisions in the United States about COVID-19 vaccination and boosters were based on data from other countries, particularly Israeli data on the Pfizer vaccine. Our study provides a precise and comprehensive characterization of the effectiveness of the three vaccines employed in the U.S. To my knowledge, this is the largest study on vaccine effectiveness, covering more than 10 million people."

In describing the implications of the study, Dr. Lin added that, "All three vaccines are durably effective against severe disease leading to hospitalization and death. Thus, unvaccinated people should get vaccinated right away." He also indicated that the Pfizer vaccine is less durable than the Moderna vaccine, so the Pfizer vaccine recipients should get boosters sooner than the Moderna vaccine recipients and that "...older adults have lower vaccine effectiveness and higher risks of hospitalization and death than younger people, so there is a greater urgency for older adults to get booster shots."

Dr. Lin also noted, "The effectiveness of the Johnson & Johnson vaccine starts to decline after 1 month, so perhaps the Johnson & Johnson vaccine recipients should be administered a second dose after 1 month; if a second dose needs to be taken soon after the first one, there is no practical advantage of taking the Johnson & Johnson vaccine."

In conclusion, Dr. Lin added, "Finally, because the majority of the vaccinees in the U.S. were vaccinated more than 7 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. Thus, vaccination and boosting is our best hope against the Omicron variant or any new variants that may arise in the future."

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