WESTERN MASS. (WGGB/WSHM) -- Most states, including Massachusetts, are extending the window for Respiratory Syncytial Virus, or RSV, immunizations. Shots for infants and toddlers will now be available through the end of April, as the virus continues to linger later than usual.

RSV typically follows a fall-to-spring pattern, with immunizations recommended through the end of March, but this season has shifted. Federal data shows positivity rates are significantly higher than this time last year.

The extension means providers can keep offering protection for a longer period. Experts say that’s critical, as RSV remains the leading cause of infant hospitalization. While it’s unclear why the virus is sticking around, doctors say continued access to immunization could make a real difference.

The latest data from the Massachusetts Department of Public Health’s Respiratory Illness Dashboard shows that Hampden County has the leading number of emergency department visits for RSV in the state.

In Western Massachusetts, that’s followed by the Berkshires with 29 visits, Hampshire County with two, and Franklin County with one.

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