This preprint retrospective study compares the effectiveness of the Moderna (mRNA-1273) and Pfizer/BioNTech (BNT162b2) vaccines from January to July 2021 in the Mayo Clinic Health System. The researchers examine effectiveness during which the highly prevalent waves of either the Alpha or Delta variant. Cohorts of vaccinated and unvaccinated individuals were matched with very similar demographic and clinical characteristics. Specifically, individuals were matched as “triples”: one unvaccinated, one vaccinated with Moderna, and one vaccinated with Pfizer/BioNTech. The matching procedure yielded 43,895 matched triples and of the 43,895 Moderna-vaccinated individuals, 35,902 were fully vaccinated; of the 43,895 Pfizer/BioNTech-vaccinated individuals, 37,573 were fully vaccinated. The unvaccinated individuals were assigned dates of hypothetical vaccination based on the actual vaccination dates of their matched partners. The results of vaccine effectiveness are presented below:
Both vaccines were highly effective against SARS-CoV-2 infection (Moderna: 86%, 95%CI: 81–90.6%; Pfizer/BioNTech: 76%, 95%CI: 69–81%) and COVID-19 associated hospitalization (Moderna: 91.6%, 95% CI: 81–97%; Pfizer/BioNTech: 85%, 95% CI: 73–93%). In July, vaccine effectiveness against hospitalization remained high (Moderna: 81%, 95% CI: 33–96.3%; Pfizer/BioNTech: 75%, 95% CI: 24–93.9%), but effectiveness against infection was lower for both vaccines (Moderna: 76%, 95% CI: 58–87%; Pfizer/BioNTech: 42%, 95% CI: 13–62%), with a more pronounced reduction for Pfizer/BioNTech vaccine. Notably, the Delta variant prevalence in Minnesota increased from 0.7% in May to over 70% in July whereas the Alpha variant prevalence decreased from 85% to 13% over the same time period.
According to the findings, the Moderna vaccine is likely more effective than the Pfizer vaccine in areas where the Delta variant is dominant and the Pfizer vaccine may have a lower durability of effectiveness. However, it is evident that both vaccines provide strong protection with severe infection and hospitalization and this is of great importance with the Delta variant. It is important to note that there are differences in the vaccines’ effectiveness in the real world relative to months prior in the pandemic. Larger and more diverse studies are needed to determine true effectiveness and to guide public health decision making.
*Note – This article is a preprint meaning findings are preliminary and the article has not been peer-reviewed.
mRNA-1273 Vaccine Efficacy in Adolescents
The incidence of COVID-19 among adolescents (ages 12-17) was approximately 900 per 100,000 during the time period of April 1 – June 11. Although rare, children can experience severe infection and with the Delta variant, children are being affected more driving the need for vaccinations for that specific population. This article in the New England Journal of Medicine evaluates the safety and efficacy of the mRNA-1273 vaccine (manufactured by Moderna) in adolescents. Scientists conducted a phase 2-3 trial to evaluate the use of the vaccine among adolescents. A total of 3,732 participants were randomly assigned in a 2:1 ratio to two groups. The first (treatment) group received the mRNA-1273 vaccine (2489 participants) and the second (control) group received a placebo (1243 participants) 28 days apart.
In order to ensure a true comparison, sociodemographic and clinical characteristics of the two groups were very similar. The mean age of the participants was 14.3 years; 51% were male, majority were White (84%), 88% were not Hispanic, and 93% had a body-mass index of less than 30. Those enrolled in the clinical trial maintained an electronic diary where they recorded adverse reactions (local and systemic) daily for seven days after each injection. The primary objective was to measure the neutralizing antibody titers and the secondary objectives were to monitor the incidence of SARS-CoV-2 infection, asymptomatic SARS-CoV-2 infection, and incidence of COVID-19 approximately 14 days after the second injection of the mRNA-1273 or the placebo. The vaccine efficacy was calculated as one minus the ratio of the incidence of cases per 1000 person-years in the vaccinated group instead of the placebo group.
The results (see figure below) showed local reactions in the mRNA-1273 group, both after the first and second injections (94.2% and 93.4%, respectively), compared to the control group (36.8% and 32.6%, respectively). Injection site pain after the first and second injections was the main reaction. Systemic adverse reactions were also reported in the vaccinated group (68.5% of the participants after the first injection and 86.1% after the second injection). Headaches, fatigue, chills, and myalgia were the most common systemic reactions. The duration of the reactions was on average 4 days and there was not much difference in reactions among those aged 12-15 years and 16-17 years. No deaths or other severe adverse events were reported. Furthermore, there were no cases of myocarditis or pericarditis.
Efficacy results are presented below. Vaccine efficacy was 93.3% (95% CI, 47.9 to 99.9) in the per-protocol population; efficacy was 39.2% (95% CI, −24.7 to 69.7) for asymptomatic infection after the second injection and 59.5% (95% CI, 28.4 to 77.3), 14 days after the first injection. For the secondary objectives of prevention of SARS-CoV-2 infection with an onset of 14 days after the second injection (in the per-protocol population) and 14 days after the first injection in the modified intention-to-treat (mITT1 ) population, the vaccine efficacy estimates for mRNA-1273 were 55.7% (95% CI, 16.8 to 76.4) and 69.8% (95% CI, 49.9 to 82.1), respectively.
The authors do note that the vaccine’s efficacy was somewhat difficult to estimate because of the low incidence of COVID-19 infection in adolescents. Overall, the results illustrate safety and efficacy of the vaccine and widespread vaccination of this specific age group could reduce morbidity and mortality related to COVID-19 and also contribute to herd immunity.