States Extend RSV Immunization Window as Virus Spreads Unusually Late Into Spring

Respiratory syncytial virus is continuing to circulate well beyond its typical seasonal window, prompting health officials across most of the United States to extend the immunization period for eligible infants and toddlers.

RSV typically peaks during the fall and winter months, but this year the virus has persisted into spring at levels high enough to concern public health authorities. The prolonged spread has led state health departments to reevaluate and extend their guidance on when children should receive RSV immunizations.

Most states have now announced extensions to the recommended immunization window, ensuring that eligible young children — particularly infants and those with underlying health conditions — can still receive protection even as the season runs longer than expected.

Health officials are urging parents and caregivers to check with their pediatricians about whether their child qualifies for RSV immunization under the updated guidelines. Nirsevimab, a monoclonal antibody approved for infants and some toddlers, remains the primary tool used to reduce the risk of severe RSV illness.

The unusual persistence of RSV this spring is part of a broader pattern of shifting respiratory virus seasons observed since the COVID-19 pandemic disrupted normal transmission cycles. Experts say surveillance data will be critical in determining how long the extended immunization period needs to remain in effect.

Parents are encouraged not to assume the RSV threat has passed simply because warmer weather has arrived. Health authorities stress that the virus can still cause serious respiratory illness in very young children, and that timely immunization remains one of the most effective ways to prevent hospitalization.