New data on COVID-19 vaccines' effectiveness over time, boosters, barriers to uptake

Multiple recent studies assessed the effectiveness of the COVID-19 vaccines at different time intervals after vaccination, while others looked at the impact of booster shots. Results of a survey suggested that racial differences in vaccine uptake may be attributable to social barriers.

An analysis of more than 8 million patients in New York State, published by the New England Journal of Medicine (NEJM) on Dec. 1, compared the effectiveness of all three FDA-authorized vaccines in May through August. The Johnson & Johnson (Janssen) vaccine had lower effectiveness than the Moderna and Pfizer-BioNTech vaccines overall, but their effectiveness among patients ages 65 years and older declined over the study period, while no time trends were seen for the effectiveness of the Johnson & Johnson vaccine in anyone, or for the Moderna and Pfizer-BioNTech vaccines in adults 18 to 64 years. A 24-week study of more than 400,000 vaccinated veterans, also published by NEJM on Dec. 1, found slightly lower risk of breakthrough infections with the Moderna vaccine than with the Pfizer-BioNTech vaccine. An accompanying editorial noted that the study's results show that both vaccines are “highly effective” and “the death rate among vaccinated persons remains tiny.”

An analysis of the Pfizer-BioNTech vaccine's effectiveness from May through September included 83,057 vaccinated adults in Israel and was published by The BMJ on Nov. 25. It found that the risk of a positive SARS-CoV-2 test increased over time beginning 90 days after vaccination, leading the authors to conclude that “consideration of a third vaccine dose might be warranted.” Another Israeli study looked at the effects of a third dose, with results published by JAMA Internal Medicine on Nov. 30. It looked at SARS-CoV-2 tests performed in patients ages 40 years or older (227,380 in those who received two doses and 272,852 in those who received three doses). The odds ratio for a positive test was 0.14 (95% CI, 0.13 to 0.15) in the 28 to 65 days following receipt of the booster. The authors noted that further monitoring “is needed to determine the duration of immunity following the booster.” A study published by The Lancet on Dec. 2 looked at mixing and matching of vaccines for booster shots and found the practice to be safe and generally effective.

A study of vaccine uptake in the U.S. as of June and July found that Black adults were less likely to be vaccinated than survey respondents of other races, but after adjustment for social factors including health insurance status, food sufficiency, income, education, and state-level political preferences, differences in vaccination rates between Black and White adults were no longer significant. Among those not yet vaccinated, Black and Hispanic adults were less vaccine hesitant than White adults, leading the authors to conclude that social barriers “could have deterred prompt COVID-19 vaccinations.” The study was published by the Journal of General Internal Medicine on Nov. 29.