The influenza vaccine evidence for this season, with numbers to quote

Design

systematic review with risk-of-bias assessment of studies published 1 August 2025 to 30 June 2026, updating a prior evidence review

Population

69 studies: 21 randomised trials, 23 comparative observational studies, 7 uncontrolled safety studies, 18 burden studies, covering older adults, pregnancy, children and immunocompromised people

Primary outcome

effectiveness and safety of US-licensed seasonal influenza vaccines

Effect

older adults, effectiveness 19-43% against hospitalisation and 29-66% against death; children aged 6 months to 17 years, 80.0% (95% CI 75.0-84.0) against influenza-associated death; high-dose vs standard-dose relative effectiveness 43.6% (95% CI 27.5-56.3)

This systematic review searched four databases for studies published between August 2025 and June 2026 on influenza epidemiology and on the effectiveness and safety of vaccines licensed in the United States, updating an earlier review. It found 69 eligible studies: 21 randomised trials, 23 comparative observational studies, seven product safety studies without a comparator and 18 descriptive burden studies, with formal risk-of-bias assessment.

The effectiveness figures are modest where the disease is commonest and high where it is most severe. In older adults, vaccine effectiveness against influenza-related hospitalisation ranged across studies from 19.0% (95% CI 0.0 to 34.0) to 43.0% (95% CI 30.0 to 53.0), and against mortality from 29.0% (95% CI 16.0 to 40.0) to 65.8% (95% CI 54.6 to 76.9). A case-cohort analysis of eight seasons of national surveillance in those aged 6 months to 17 years found effectiveness of 80.0% (95% CI 75.0 to 84.0) against laboratory-confirmed influenza-associated death. Vaccination in pregnancy was associated with 44.4% effectiveness (95% CI 31.4 to 54.9) against symptomatic disease in infants. Randomised data for 2022 to 2025 showed the high-dose vaccine outperformed standard dose against hospitalisation in older adults, relative effectiveness 43.6% (95% CI 27.5 to 56.3).

On safety, a self-controlled case series covering 9,973,703 vaccinated people found no increase in serious adverse events, including Guillain-Barre syndrome, whether influenza vaccine was given alone or alongside RSV or COVID-19 immunisation. A separate series found no increase in febrile seizures in the seven days after vaccination.

These are useful numbers precisely because they are unglamorous. Being able to say that the vaccine cuts the risk of a child dying of influenza by about four-fifths, and that coadministration with other seasonal vaccines has been checked in nearly ten million people, is more persuasive than any general reassurance. Note that this is US-licensed formulations and US epidemiology; circulating strains and timing differ in India, where influenza follows the monsoon in much of the country rather than a winter season.

• Quote the paediatric figure when parents hesitate: about 80% effectiveness against influenza-associated death in children and adolescents
• Offer the high-dose formulation to older adults where it is available, on randomised evidence of better protection against hospitalisation
• Coadminister with RSV and COVID-19 vaccines without hesitation on safety grounds; nearly ten million records show no signal
• Vaccinate in pregnancy, which protects the infant as well as the mother
• Adjust timing to local epidemiology: much of India sees influenza around the monsoon rather than in winter

The statistics, in plain English

The wide ranges reflect different seasons and different study designs rather than uncertainty within any one estimate: influenza vaccine effectiveness genuinely varies year to year with how well the strains match. One of the hospitalisation estimates has a lower bound of 0.0%, meaning that particular study could not exclude no effect at all, which is why the range rather than a single pooled figure is reported. Self-controlled case series compare each person against themselves at different times, which removes confounding by fixed personal characteristics and is well suited to detecting rare vaccine adverse events; a null result across 9,973,703 people is strong evidence that any increase, if it exists, is very small.

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