mRNA vaccines ease breakthrough COVID; Novavax helps block variant
The few adults who receive a COVID-19 mRNA vaccine but still become infected have a milder, shorter illness and lower viral RNA loads than their unvaccinated peers, finds a real-world US study yesterday in the New England Journal of Medicine.
The journal also features a UK study confirming that the Novavax vaccine offers 90% overall effectiveness and protects against the highly transmissible and potentially more deadly Alpha (B117) SARS-CoV-2 variant.
mRNA vaccines 91% effective after 2 doses
In the first study, a team led by the Centers for Disease Control and Prevention COVID-19 Response Team tested 3,975 coronavirus-naïve healthcare workers, first responders, and other essential workers who received one or two doses of the Pfizer/BioNTech or Moderna mRNA vaccine or were unvaccinated from Dec 14, 2020, to Apr 10, 2021. The study took place in Arizona, Florida, Minnesota, Oregon, Texas, and Utah.
Of the participants, 3,179 (80%) received at least one dose by the end of the data-collection period, while 2,686 (84%) were given two doses. Of the vaccines, 67% were Pfizer and 33% were Moderna, while the brand name wasn’t recorded in less than 1%.
In total, 204 (5%) tested positive for COVID-19, of whom 5 were fully vaccinated, 11 were partially vaccinated, and 156 were unvaccinated. The 32 remaining participants had an undetermined vaccination status and were excluded from the analysis.
In fully vaccinated participants, adjusted vaccine effectiveness was 91% (95% confidence interval [CI], 76% to 97%), falling to 81% (95% CI, 64% to 90%) in the partially vaccinated group.
Fully or partially vaccinated participants had a 40% lower average viral RNA load (95% CI, 16% to 57%) than the unvaccinated group, a 58% lower risk of fever (relative risk, 0.42; 95% CI, 01.8 to 0.98), and a shorter illness (-6 days of symptoms, -2 days spent sick in bed; 95% CI, 0.8 to 3.7).