COVID vaccines are safe and effective
COVID vaccines reduce severe illness, hospital treatment and deaths. Updated doses can add protection after earlier vaccination or infection. Protection against infection fades. Serious side effects are rare; benefits and risks depend on age, health and vaccine.
- A 2025–26 adult study estimated 55% protection against COVID hospitalization versus no current-season dose. [1]US adults, September–December 2025; short follow-up.
- Updated vaccination can add protection after earlier vaccination or infection. [1][2]
- Protection against serious illness can remain even when infection occurs. [1][2]
On this page
Updated vaccines can add protection
In a US study of adults without immune suppression, a 2025–26 dose was associated with 55% lower risk of COVID hospitalization than no current-season dose (95% confidence interval 41–66%). Encounters were from September–December 2025, with a median 46 days since vaccination. This is relative effectiveness from an observational comparison—not a 55-percentage-point reduction or a year-long estimate for everyone.
Infection and serious illness are different outcomes
Protection against infection is incomplete and fades. Earlier infection also contributes immunity. The useful question is how much an updated dose adds against a particular outcome. A separate study of mostly older male US veterans found protection against hospitalization and death; it cannot supply a young healthy person’s absolute benefit.
Safety and side effects
Most reactions pass quickly. Myocarditis is a real, rare risk after mRNA vaccines, with higher risk in adolescent and young adult males and differences by product and dose. Infection does not always carry more myocarditis risk than every vaccine dose in every subgroup.
Large studies test claims of widespread harm
A French study of adults aged 18–59 found no increased overall mortality over nearly four years. Differences between vaccinated and unvaccinated people can affect the comparison. The deaths page explains both this population evidence and rare fatal reactions; cancer and pregnancy have their own evidence pages.
COVID vaccines reduce severe illness, hospital treatment and deaths.
Keep in mind
- The findings apply to the vaccines, populations and outcomes studied. Personal recommendations depend on your health and current local guidance.
Find the answer you need
Sources you can check
Publication links open in a new tab, so you can keep your place here.
Interim Estimated Effectiveness of 2025–2026 COVID-19 Vaccines in Adults Using a Test-Negative Design (opens in a new tab)
JAMA Network Open, 2026
US immunocompetent adults, September–December 2025; compares a current-season dose with none, with short follow-up.
Return to reading ↑Association of 2024–2025 Covid-19 Vaccine with Covid-19 Outcomes in U.S. Veterans (opens in a new tab)
New England Journal of Medicine, 2025
Observational US veteran study with a flu-vaccinated comparator; mostly older men, not every age group.
Return to reading ↑FDA Approves Required Updated Warning in Labeling of mRNA COVID-19 Vaccines Regarding Myocarditis and Pericarditis (opens in a new tab)
FDA, June 2025
Observed 2023–24-formulation incidence in days 1–7 is not an excess-risk estimate. Persistent MRI findings have uncertain long-term meaning.
Return to reading ↑Risk of Myocarditis After Sequential Doses of COVID-19 Vaccine and SARS-CoV-2 Infection by Age and Sex (opens in a new tab)
Circulation, 2022
Historical English estimates use 28-day windows and vary by age, sex, product and dose; not current booster rates.
Return to reading ↑COVID-19 mRNA Vaccination and 4-Year All-Cause Mortality Among Adults Aged 18 to 59 Years in France (opens in a new tab)
JAMA Network Open, 2025
Large observational comparison, median 45 months. Selection and health differences can affect all-cause mortality; does not settle pediatric risk.
Return to reading ↑
Detailed research notes and source data
Our longer notes explain how we checked the studies, including disagreements and documents we could not get.
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These pages have not completed expert review. For personal vaccine advice, talk to a clinician who knows your circumstances.
Research checked: . Wording reviewed: 2026-10-15. Version: vaccine-2026-10-15.
We revisit the page when new evidence or corrections change the answer. A public history of corrections is not available yet.