Latest COVID-19 research looks at vaccines' efficacy, thrombocytopenia risk

An analysis of thrombosis with thrombocytopenia syndrome (TTS) cases among recipients of COVID-19 vaccines found that this complication was associated with the Johnson & Johnson (Janssen) vaccine, but not the mRNA vaccines. The series, published by Annals of Internal Medicine on Jan. 18, included 57 TTS cases, 54 occurring in patients who received the J&J vaccine (a rate of 3.83 per million vaccine doses vs. 0.00855 per million with the mRNA-based vaccines). The median age among the 54 patients was 44.5 years, while the three TTS cases after mRNA vaccination all occurred in patients older than age 50 years. The study authors said that TTS “is a rare but serious adverse event” associated with the Johnson & Johnson vaccine. “The different demographic characteristics of the 3 cases reported after mRNA-based COVID-19 vaccines and the much lower reporting rate suggest that these cases represent a background rate,” they concluded. The authors also noted that TTS diagnosis can be challenging and may require repeated imaging. An accompanying editorial noted that the findings support the CDC's decision to favor the mRNA-based vaccines and “help to illuminate further the evolving picture of the clinical spectrum and epidemiology of anti-PF4 disorders.”

Three studies, all published by the New England Journal of Medicine on Jan. 12, looked at the effectiveness of the COVID-19 vaccines. An analysis of more than 10 million people in North Carolina found that effectiveness against COVID-19 at seven months after vaccination was 66.6% (95% CI, 65.2% to 67.8%) for the Pfizer-BioNTech vaccine and 80.3% (95% CI, 79.3% to 81.2%) for the Moderna vaccine, while the J&J vaccine was 59.4% (95% CI, 57.2% to 61.5%) effective at five months. All three vaccines maintained better effectiveness in preventing hospitalization and death, the authors noted. “Waning protection against infection over time was due to both declining immunity and the emergence of the delta variant,” they concluded. An analysis from England looked at protection with the Pfizer-BioNTech vaccine (as well as the AstraZeneca vaccine) after 20 weeks, finding it to be 91.7% effective (95% CI, 90.2% to 93.0%) against hospitalization and 91.9% effective (95% CI, 88.5% to 94.3%) against death from COVID-19. A study of adolescents found that the Pfizer-BioNTech vaccine was 98% effective against ICU admission, and all seven study deaths occurred in patients who were unvaccinated.

Finally, an industry-funded trial, published by JAMA on Jan. 14, found that the antibody combination of casirivimab and imdevimab reduced progression from asymptomatic to symptomatic infection among household contacts of COVID-19 patients. Among 204 patients in the primary efficacy analysis, the rate of symptomatic infection was 29.0% in those randomized to a subcutaneous injection of the combination drug versus 42.3% in those given placebo (odds ratio, 0.54 [95% CI, 0.30 to 0.97]; P=0.04). The drug was also associated with a 5.6-day reduction in symptom duration per symptomatic participant. An accompanying editorial offered several caveats, including that casirivimab and imdevimab are not active against the omicron variant. “If, in the future, casirivimab and imdevimab therapy is authorized for use in people who are infected but do not have symptoms, this monoclonal antibody combination could potentially be used in high-risk situations, such as for immunosuppressed individuals who are RT-PCR positive but asymptomatic,” the editorial said. The therapies that do work for outpatients with COVID-19 in the omicron era were reviewed in a Viewpoint, also published by JAMA on Jan. 14.