Flu, COVID and RSV vaccines: what the evidence shows on protection and risks as the 2026-27 season begins

Autumn is when three respiratory viruses begin to circulate together in the northern hemisphere: influenza, the coronavirus that causes COVID-19, and respiratory syncytial virus (RSV). Vaccines exist for all three. In the United States this year, the advice on who gets them is coming from an unfamiliar direction.

Major medical groups have released their vaccine recommendations for the 2026-2027 respiratory virus season, Scripps News reported in September 2026. In the past such guidance came from a federal advisory committee. “The single biggest change is that the recommendations are not now coming from the federal government. They’re coming from professional societies of various different doctors,” said Amesh Adalja, a senior scholar at the Johns Hopkins Center for Health Security.

Behind the argument over who decides is a simpler question of what the vaccines do. This explainer sets out the measured protection and the measured risks for each.

Why an independent review of flu, COVID and RSV vaccines was done

The fullest recent summary of the evidence was not produced by a government agency. A group of physicians and epidemiologists led from Stanford University School of Medicine and Massachusetts General Hospital carried out its own systematic review, meaning a structured search for every relevant study, and published it in the New England Journal of Medicine in October 2025.

Their stated reason was the policy situation. Changes in the vaccine advisory process in the United States have disrupted immunization guidance, they wrote, which made independent review necessary. They updated the federal committee’s last full evidence review, done in 2023 and 2024, by searching for everything published since. Of 17,263 identified references, 511 studies met the inclusion criteria.

The measure they report most often is vaccine effectiveness against hospitalization. A figure of 50% means that vaccinated people were hospitalized with the disease at half the rate of comparable unvaccinated people. When the same calculation comes from a randomized trial, it is called efficacy. Most of the review’s estimates come from observational studies that compare the two groups as they are found, a point with consequences taken up below.

How well the flu vaccine works

Influenza vaccination had a pooled vaccine effectiveness of 48% in adults between the ages of 18 and 64 years and 67% in children against hospitalization, with ranges of 39% to 55% and 58% to 75%.

Flu vaccines are reformulated every year, because the virus changes, and the match is better in some years than others. A snapshot from one season shows the spread. In early 2025 the Centers for Disease Control and Prevention (CDC) published interim results from four monitoring networks. In children and adolescents, effectiveness was 63% and 78% against influenza-associated hospitalization (two networks). In adults it was lower, at 41% and 55% against influenza-associated hospitalization (two networks).

Older adults respond less strongly to standard flu vaccines, which is why stronger versions were developed. The main trial of a high-dose vaccine enrolled people aged 65 and over: a total of 31,989 participants were enrolled from 126 research centers in the United States and Canada. Over the season, 1.4% of those given the high-dose vaccine and 1.9% of those given the standard dose had laboratory-confirmed influenza caused by any viral type or subtype. That is a difference of five cases per 1,000 people. The trial put the relative reduction at 24.2%. The trial was funded by the vaccine’s manufacturer.

How well COVID-19 vaccines work

For COVID-19 the review pooled studies of the vaccines used in recent seasons. Those vaccines had pooled vaccine effectiveness against hospitalization of 46% among adults in studies that followed vaccinated and unvaccinated people forward in time, and 50% in studies that started with hospital patients and looked back at who had been vaccinated. Among immunocompromised adults, people whose immune systems are weakened by illness or treatment, the figure was 37%.

These numbers measure added protection. They compare people who had a recent dose with people who did not, whatever immunity either group already carried from past infection or vaccination.

Formulations are updated to follow the virus. For one of the newer versions the review found a single study, which estimated effectiveness at 68% with a range of 42% to 82%. That is a wide interval from limited data.

The known serious risk is myocarditis, inflammation of the heart muscle, which is concentrated in young males. The diagnosis occurred at rates of 1.3 to 3.1 per 100,000 doses in male adolescents, with lower risk associated with longer dosing intervals.

How well RSV vaccines and antibodies work

RSV is the newest of the three to have vaccines. The virus causes cold-like illness in most people and can be dangerous at the two ends of life, in young infants and in the old.

The review treated three products together, one of them an antibody injection for infants called nirsevimab. 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. Each rests on a large randomized trial.

For older adults, one trial enrolled people aged 60 and over, and a total of 24,966 participants received one dose of the vaccine or placebo. Over a median of 6.7 months there were 7 cases of RSV lung infection in the vaccine group and 40 in the placebo group, an efficacy of 82.6% with a range of 57.9% to 94.1%. The incidences of serious adverse events and potential immune-mediated diseases were similar in the two groups. Immune-mediated diseases are conditions in which the immune system attacks the body’s own tissue.

Infants can be protected in two ways. The first is to vaccinate the mother late in pregnancy so that her antibodies cross to the baby. In the trial of that approach, 3682 maternal participants received vaccine and 3676 received placebo. Severe RSV illness needing medical attention occurred within 90 days of birth in 6 infants of women in the vaccine group and 33 infants of women in the placebo group. By 180 days the counts were 19 and 62. No safety signals were detected in maternal participants or in infants and toddlers up to 24 months of age. A safety signal means a health problem turning up more often than expected.

The second way is nirsevimab, which is an antibody and not a vaccine. It is a laboratory-made protein that blocks the virus directly, given to the infant as one injection. A trial in France, Germany and the United Kingdom tested it in ordinary care. A total of 8058 infants were randomly assigned to receive nirsevimab (4037 infants) or standard care (4021 infants). Eleven infants (0.3%) in the nirsevimab group and 60 (1.5%) in the standard-care group were hospitalized for RSV lung infection. That is 12 fewer hospital admissions for every 1,000 babies treated. Treatment-related adverse events occurred in 86 infants (2.1%) in the nirsevimab group.

All three RSV trials were funded by the companies that make the products.

One RSV vaccine carries a rare neurological risk in older adults. It was associated with 18.2 excess cases of Guillain-Barré syndrome per million doses in older adults, the review found. Guillain-Barré syndrome is a condition in which the immune system attacks the nerves, causing weakness that is usually temporary and occasionally severe. For the vaccine given in pregnancy, the review did not find a link with preterm birth when it was given at 32 to 36 weeks.

What the vaccine evidence adds up to

Immunization	Protection found	Main measured risk
Flu vaccine	48% against hospitalization in adults 18 to 64; 67% in children	None highlighted in the review
COVID-19 vaccine	46% to 50% against hospitalization in adults; 37% if immunocompromised	Myocarditis, 1.3 to 3.1 per 100,000 doses in male adolescents
RSV vaccine, adults 60 and over	68% or more against hospitalization	Guillain-Barré syndrome, 18.2 excess cases per million doses of one vaccine
RSV vaccine in pregnancy	6 against 33 severe infant cases by 90 days in the trial	None detected in the trial
Nirsevimab for infants	11 against 60 hospitalizations among 8,058 infants	Treatment-related events in 2.1%

The reviewers’ overall judgment was that safety profiles were consistent with previous evaluations. Their conclusion was that ongoing peer-reviewed evidence supports the safety and effectiveness of immunizations against COVID-19, RSV, and influenza during the 2025-2026 season.

What medical societies recommend for flu, COVID and RSV vaccines

The recommendations for this season, as reported by Scripps News, are these.

The American Medical Association and several leading specialty groups, including family physicians, pediatricians, infectious disease specialists and obstetricians, are aligned on the flu vaccine: it is recommended for everyone 6 months and older.

On COVID-19 some of the groups go further than the federal agency. While the CDC recommends parents of children under 18 consult their doctor, several specialty groups recommend vaccination for children aged 6 to 23 months. For children ages 2 to 18, those groups recommend vaccination if the child is at high risk of severe COVID infection.

On RSV the target groups are narrower. RSV vaccines are primarily recommended for newborns, pregnant women, and adults 75 and older. Newborns are not vaccinated themselves: their protection comes from the vaccine given in pregnancy or from the antibody injection. The age for older adults is also narrower than in the trial described above, which enrolled people from 60. Obstetricians are focused on pregnant women, noting the RSV season now runs from September through March, an extension from the previous September-to-January window.

Which of these applies to an individual depends on age, pregnancy and medical conditions, which is assessed by their doctor.

What the evidence on flu, COVID and RSV vaccines leaves open

The review’s effectiveness figures are mostly observational. People who choose vaccination differ from those who do not in age, health and how readily they seek care, and those differences can inflate or shrink an estimate. Study designs try to correct for this and cannot do so completely.

The figures look backward. The review was published in October 2025 and pooled studies of vaccines given in the seasons before it. Flu and COVID-19 vaccines are changed regularly, and how well this season’s versions match the viruses that circulate will be known only in retrospect.

Protection is not permanent. Hospitalization estimates describe the months after a dose, and the RSV trial in older adults reported a median of 6.7 months of follow-up.

The randomized trials are strong on design and were paid for by manufacturers. Their main outcomes are infections and hospital admissions, not deaths.

The review itself was funded by the Center for Infectious Disease Research and Policy and the Alumbra Innovations Foundation, and its authors include Rochelle Walensky, a former director of the CDC.

Pooled studies show these vaccines cutting hospitalizations by about half for flu and COVID-19 and by two-thirds or more for RSV, on evidence that is mostly observational and describes earlier seasons’ vaccines.