The global health burden of COVID-19 remains significant. Consequently, researchers continue to study the most effective ways to protect adults from the Omicron variant. A recent rapid review for the American College of Physicians explores Omicron-adapted vaccine effectiveness across different demographics. This evidence helps clinicians determine the optimal timing for booster doses in their patients.
Timing and Omicron-adapted vaccine effectiveness
The review found that vaccination significantly reduces both all-cause mortality and COVID-19-related hospitalizations. Specifically, the benefit appears most pronounced when patients receive a dose more than 365 days after their prior vaccination. In these cases, the vaccine effectiveness against mortality reached roughly 36%. However, when physicians administer the dose earlier, the data shows no significant difference in hospitalization outcomes. Therefore, clinical timing remains a crucial factor for achieving the best protection.
Safety and Myocarditis Risk in Older Adults
While these vaccines provide clear benefits, clinicians must also consider potential harms. For instance, the review noted a potential increase in myocarditis among adults aged 50 years or older. Specifically, the data showed an incidence rate ratio of 2.7 for this group. Although this evidence carries low certainty, it suggests a need for vigilant monitoring. Moreover, most other serious adverse events did not differ significantly between the vaccine types studied.
Comparing Next-Generation mRNA Vaccines
The review also compared the mRNA-1283.222 bivalent vaccine with mRNA-1273.222. In adults of all ages, the data showed no meaningful difference in all-cause mortality or serious adverse events. Both vaccines appear to offer comparable safety and efficacy profiles for the general adult population. Consequently, clinicians can feel confident using either formulation based on availability. Additionally, researchers continue to monitor long-term outcomes for these next-generation products.
Frequently Asked Questions
Q1: Does timing affect Omicron-adapted vaccine effectiveness?
Yes, effectiveness against mortality and hospitalization improves significantly when the booster interval exceeds 365 days.
Q2: Is there a risk of myocarditis in patients over 50?
Evidence suggests a possible increase in myocarditis among adults aged 50 and older, though the certainty remains low.
Q3: How do the different bivalent mRNA vaccines compare?
The mRNA-1283.222 and mRNA-1273.222 vaccines show no significant differences in mortality or serious adverse event rates.
References
- Dobrescu A et al. Effectiveness, Comparative Effectiveness, and Harms of COVID-19 Vaccines in Adults Who Are Not Pregnant or Immunocompromised: A Rapid Review for the American College of Physicians. Ann Intern Med. 2026 Feb 24. doi: 10.7326/ANNALS-25-05044. PMID: 41730209.
- Moderna. Phase 3 Data for mRNA-1283.222 and mRNA-1273.222 Comparison. 2024.
- US Centers for Disease Control and Prevention. Clinical Guidance for COVID-19 Vaccination. 2025.