A new study has found that annual COVID-19 booster vaccinations continue to provide significant protection against severe illness, even among people who already have immunity from previous infections, vaccinations, or both.
Researchers analyzed data from more than 110,000 emergency department visits and hospital admissions across seven U.S. states between September and December 2025. The findings showed that adults who received the updated 2025–2026 COVID-19 vaccine were approximately 55 percent less likely to be hospitalized with COVID-19 and 50 percent less likely to require emergency or urgent medical care compared with those who did not receive the booster.
The study comes as health authorities worldwide evaluate the effectiveness of ongoing COVID-19 vaccination programs in populations that have experienced multiple waves of infection and widespread vaccine coverage. The results suggest that updated booster doses continue to provide an important layer of protection beyond existing immunity.
Researchers noted that many participants likely had residual protection from earlier vaccinations, previous COVID-19 infections, or a combination of both. Despite this background immunity, the updated vaccine still demonstrated meaningful effectiveness in reducing the risk of severe disease and healthcare visits.
The vaccine formulation examined in the study was updated to target the JN.1 family of COVID-19 variants following recommendations from U.S. health regulators in 2025. Descendants of the JN.1 variant continue to circulate globally, making updated protection particularly relevant for vulnerable populations.
Experts say the findings reinforce the value of annual booster campaigns, especially for older adults, people with underlying health conditions, and others at higher risk of serious complications from COVID-19. The study also suggests that vaccine-induced protection remains beneficial even as natural immunity from prior infections becomes more widespread.
As COVID-19 transitions from a pandemic emergency to an ongoing public health challenge, the research provides evidence that updated annual boosters can help reduce hospitalizations and lessen the burden on healthcare systems. The findings support continued vaccination efforts aimed at protecting high-risk groups and preventing severe outcomes from future waves of infection.
