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COVID-19* / epidemiology

Updated Evidence for Covid-19, RSV, and Influenza Vaccines for 2025–2026

Author/s: 
Michael S. Abers, Jake Scott, Harleen K. Marwah, Nicole C. McCann, Eric A. Meyerowitz, Aaron Richterman, Derek F. Fleming, Caitlin M. Dugdale

Background: Changes in the vaccine advisory process in the United States have disrupted immunization guidance, which reinforces the need for independent evidence review to inform decisions regarding immunization for respiratory viruses during the 2025-2026 season.

Methods: We conducted a systematic review of U.S.-licensed immunizations against coronavirus disease 2019 (Covid-19), respiratory syncytial virus (RSV), and influenza. We searched databases on PubMed/MEDLINE, Embase, and Web of Science for updates of the most recent review by the Advisory Committee on Immunization Practices (ACIP) Evidence-to-Recommendations for each disease, which was performed during the 2023-2024 period. Outcomes included vaccine efficacy and effectiveness against hospitalization, other clinical end points, and safety.

Results: Of 17,263 identified references, 511 studies met the inclusion criteria. Covid-19 mRNA vaccines against the XBB.1.5 subvariant had pooled vaccine effectiveness against hospitalization of 46% (95% confidence interval [CI], 34 to 55; from cohort studies) and 50% (95% CI, 43 to 57; from case-control studies) among adults and 37% (95% CI, 29 to 44) among immunocompromised adults. In a case-control study, vaccines against the KP.2 subvariant showed an effectiveness of 68% (95% CI, 42 to 82). Maternal RSV vaccination (for infant protection), nirsevimab for infants, and RSV vaccines in adults who were 60 years of age or older showed vaccine effectiveness of 68% or more against hospitalization. Influenza vaccination had a pooled vaccine effectiveness of 48% (95% CI, 39 to 55) in adults between the ages of 18 and 64 years and 67% (95% CI, 58 to 75) in children against hospitalization. Safety profiles were consistent with previous evaluations. The diagnosis of myocarditis associated with Covid-19 vaccines occurred at rates of 1.3 to 3.1 per 100,000 doses in male adolescents, with lower risk associated with longer dosing intervals. The RSVpreF vaccine was associated with 18.2 excess cases of Guillain-Barré syndrome per million doses in older adults; a significant association with preterm birth was not observed when the vaccine was administered at 32 to 36 weeks' gestation.

Conclusions: Ongoing peer-reviewed evidence supports the safety and effectiveness of immunizations against Covid-19, RSV, and influenza during the 2025-2026 season. (Funded by the Center for Infectious Disease Research and Policy and the Alumbra Innovations Foundation.).

Keywords 
COVID-19 vaccine COVID-19 'Vaccination vaccines

The 2024 National Academies of Sciences, Engineering, and Medicine Long COVID Definition: What Clinicians Need to Know

Author/s: 
Lily Chu, Karyn Bishof, Abigail A Dumes, E Wesley Ely, Paule V Joseph, Andrea B Troxel

Millions of Americans affected by Long COVID (LC) report difficulty accessing care and support. One barrier is obtaining a diagnosis. In response, US federal agencies commissioned a National Academies of Sciences, Engineering, and Medicine (NASEM) committee to re-examine the existing federal definitions for LC. The Committee concluded that LC is "an infection-associated chronic condition (IACC) occurring after SARS-CoV-2 infection that is present for at least 3 months as a continuous, relapsing and remitting, or progressive disease state that can present as singular or multiple symptoms and/or diagnosable conditions." The full report was released in June 2024. We briefly highlight features and aspects of the definition that may help clinicians identify those who remain undiagnosed and improve care for all LC patients.

Keywords 
COVID-19 Long COVID post-acute sequelae of COVID-19

Nirmatrelvir or Molnupiravir Use and Severe Outcomes From Omicron Infections

Author/s: 
Lin, Dan-Yu, Huang, Shuaiqi, Abi Fadel, Francois

Question: What outcomes are associated with ritonavir-boosted nirmatrelvir or molnupiravir use for outpatient treatment of SARS-CoV-2 Omicron subvariants, particularly BQ.1.1 and XBB.1.5, in high-risk individuals?

Findings: In a cohort study of 68 867 patients who received a diagnosis of COVID-19 at Cleveland Clinic from April 1, 2022, to February 20, 2023, and who were at high risk of progressing to severe COVID-19, both nirmatrelvir and molnupiravir use were significantly associated with reductions in hospitalization and death. The association was observed across subgroups defined by age, race and ethnicity, date of diagnosis, vaccination status, previous infection status, and coexisting conditions.

Meaning: These findings suggest that both nirmatrelvir and molnupiravir can be used to treat nonhospitalized patients who are at high risk of progressing to severe COVID-19.

Keywords 
COVID-19 Ritonavir Molnupiravir COVID-19 variants

Evaluation of Waning of SARS-CoV-2 Vaccine–Induced Immunity

Author/s: 
Menegale, Francesco, Manica, Mattia, Zardini, Agnese, Guzzetta, Giorgio, Marziano, Valentina, d'Andrea, Valeria, Trentini, Filippo, Ajelli, Marco, Poletti, Piero, Merler, Stefano

Importance Estimates of the rate of waning of vaccine effectiveness (VE) against COVID-19 are key to assess population levels of protection and future needs for booster doses to face the resurgence of epidemic waves.

Objective To quantify the progressive waning of VE associated with the Delta and Omicron variants of SARS-CoV-2 by number of received doses.

Data Sources PubMed and Web of Science were searched from the databases’ inception to October 19, 2022, as well as reference lists of eligible articles. Preprints were included.

Study Selection Selected studies for this systematic review and meta-analysis were original articles reporting estimates of VE over time against laboratory-confirmed SARS-CoV-2 infection and symptomatic disease.

Data Extraction and Synthesis Estimates of VE at different time points from vaccination were retrieved from original studies. A secondary data analysis was performed to project VE at any time from last dose administration, improving the comparability across different studies and between the 2 considered variants. Pooled estimates were obtained from random-effects meta-analysis.

Main Outcomes and Measures Outcomes were VE against laboratory-confirmed Omicron or Delta infection and symptomatic disease and half-life and waning rate associated with vaccine-induced protection.

Results A total of 799 original articles and 149 reviews published in peer-reviewed journals and 35 preprints were identified. Of these, 40 studies were included in the analysis. Pooled estimates of VE of a primary vaccination cycle against laboratory-confirmed Omicron infection and symptomatic disease were both lower than 20% at 6 months from last dose administration. Booster doses restored VE to levels comparable to those acquired soon after the administration of the primary cycle. However, 9 months after booster administration, VE against Omicron was lower than 30% against laboratory-confirmed infection and symptomatic disease. The half-life of VE against symptomatic infection was estimated to be 87 days (95% CI, 67-129 days) for Omicron compared with 316 days (95% CI, 240-470 days) for Delta. Similar waning rates of VE were found for different age segments of the population.

Conclusions and Relevance These findings suggest that the effectiveness of COVID-19 vaccines against laboratory-confirmed Omicron or Delta infection and symptomatic disease rapidly wanes over time after the primary vaccination cycle and booster dose. These results can inform the design of appropriate targets and timing for future vaccination programs.

Keywords 
COVID-19 COVID-19 vaccine 'Vaccination
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