Landmark Review Offers Clarity on COVID, RSV, and Flu Vaccine Effectiveness for 2025-26 Season
A comprehensive systematic review published in the New England Journal of Medicine provides crucial evidence-based guidance for navigating the upcoming 2025-26 respiratory virus season, a task made more urgent by disruptions in federal vaccine advisory processes. Analyzing data from 511 studies, researchers emphasize the need for independent evidence synthesis to inform clinicians, public health officials, and patients as they make critical decisions about immunization.
Understanding the Evolving Landscape of Respiratory Virus Protection
The review highlights that interpreting vaccine effectiveness requires acknowledging the unique immunological context surrounding each virus – COVID-19, respiratory syncytial virus (RSV), and influenza. “The effectiveness percentages we report tell different stories, depending on which virus we’re addressing,” researchers noted. COVID-19 vaccines function within populations already possessing complex immunity from prior infection and vaccination, RSV immunizations target adults often previously infected but vaccine-naive, and influenza vaccines contend with the constant challenge of viral strain variation.
COVID-19 Vaccines: Boosting Existing Immunity
Current COVID-19 vaccines, such as the KP.2 formulation, demonstrate 46% to 50% effectiveness against hospitalization (IVY/VISION networks, 2024-25). However, this figure represents additional protection layered on top of widespread background immunity acquired through prior infection and vaccination. The composition of “unvaccinated” groups is increasingly complex, encompassing individuals who have never been vaccinated, those with outdated vaccinations, and those with natural immunity from prior infection.
A Veterans Affairs (VA) study revealed a 68% effectiveness against hospitalization with the KP.2 vaccine, a significant improvement from the 32% observed during JN.1 dominance with the previous formulation. This underscores the importance of matching vaccines to circulating strains, even in populations with pre-existing immunity. For immunocompromised adults, the vaccine still offers clinically significant protection, reducing hospitalization risk by 37%. Effectiveness has fluctuated with viral evolution, mirroring the pattern seen with influenza.
RSV: Robust Protection, Especially for Vulnerable Groups
RSV immunizations show particularly strong results, with 75% to 80% effectiveness against hospitalization in adults aged 60 and older. This higher efficacy stems from the comparison between immunized and immunization-naive individuals – those previously exposed to RSV but never vaccinated against it. This represents a closer approximation of absolute protection than the incremental gains observed with COVID-19 vaccines.
Breakthrough prevention strategies are also emerging for infants. Maternal immunization with the RSVpreF (Abrysvo) vaccine achieved 68% effectiveness against infant hospitalization through antibody transfer, while Nirsevimab, a long-acting monoclonal antibody, demonstrated 80% to 85% effectiveness against hospitalization and intensive care unit admission. These advancements are transformative, addressing a virus that previously hospitalized 60,000 to 160,000 older adults and countless infants annually.
Flu Vaccines: Variable, Yet Valuable
Influenza vaccines in the review showed pooled effectiveness of 67% against hospitalization in children, 48% in working-age adults, and 42% to 53% in older adults. Effectiveness varies year-to-year depending on the vaccine-strain match, ranging from 20% to 30% in years with poor matches to over 60% when the match is good. Enhanced formulations consistently outperform standard doses for older adults, supporting their preferential use.
Safety Remains Reassuring
An extensive safety analysis encompassing millions of vaccine recipients offers reassurance. Myocarditis following mRNA COVID-19 vaccination remains rare, particularly in adolescent and young adult males, and rates are significantly lower than those observed in 2021. No new or increased myocarditis risks were identified with XBB.1.5 vaccines, and the risk remains lower than that associated with COVID-19 infection itself.
Pregnancy safety data from seven large observational studies revealed no increased risk of miscarriage or stillbirth with COVID-19 vaccination, and even demonstrated protective associations with lower rates of preterm birth and low birthweight.
Regarding RSV vaccines, initial data indicated a potential link between the RSVpreF vaccine and Guillain-Barré syndrome (GBS), a rare nerve disorder, with 18.2 excess cases per million doses. However, subsequent analysis by the Food and Drug Administration (FDA) estimated approximately 9 excess cases per million doses for RSVpreF and 7 per million for RSVPreF3-AS01, prompting the addition of GBS warnings to both vaccines’ labels in January 2025. Despite this, the benefit-risk balance remains strongly favorable given the substantial hospitalization and mortality burden of RSV in older adults. Initial concerns regarding preterm birth with maternal RSV vaccination have not materialized in real-world studies when vaccination occurs between 32 and 36 weeks of pregnancy.
Tailoring Protection to Individual Risk
The critical takeaway for healthcare providers and patients is that the level of additional protection offered by each immunization varies significantly based on individual circumstances. A healthy 30-year-old with robust COVID-19 immunity faces a different risk-benefit profile than a 75-year-old confronting RSV. COVID-19 vaccine effectiveness represents incremental benefit in a largely immune population, while RSV immunization provides substantial protection in vaccine-naive older adults. Influenza vaccines offer variable but meaningful protection against a constantly evolving target. Despite these differences, all three immunizations demonstrably reduce the risk of severe disease.
Independent Evidence in an Era of Uncertainty
This systematic review underscores the enduring value of rigorous, transparent evidence synthesis, particularly when traditional advisory processes are disrupted. All data are publicly available through an interactive web application to promote transparency and trust. The landscape of immunity has fundamentally changed since 2020, necessitating evolving tools for measuring and understanding vaccine impact.
In an era of disrupted federal guidance, this independent synthesis provides the evidence foundation needed to navigate the 2025-26 respiratory season. The numbers tell different stories for different vaccines in different populations, and it is our collective task to ensure those stories are understood accurately, empowering individuals to make informed decisions based on their unique circumstances.
