RSV activity remains elevated for this time of year, prompting health officials to extend the immunization window later into spring, through the end of April in many regions.

The virus spreads via droplets or direct contact; while symptoms can mimic a cold, RSV can lead to serious disease in vulnerable populations.

Despite the seasonal shift, the CDC notes that RSV’s overall severity remains comparable to previous years.

Each year, about two to three percent of infants under 3 months are hospitalized with RSV, illustrating the ongoing impact of the virus.

While the exact cause of RSV’s persistence isn’t clear, extending immunization access is a key response to continued transmission.

The American Academy of Pediatrics backs monoclonal antibody immunization for infants, with a CDC study finding lower RSV-related hospitalizations during 2024-25 when these immunizations were available.

The extension aims to sustain protection as RSV remains the leading cause of infant hospitalization, even as the season shifts and overall severity mirrors prior years.

While the reasons for the shifted RSV season aren’t fully known, possible factors include environmental, biological, and behavioral influences such as timing of doctor visits and indoor climate.

RSV is highly contagious and spreads through droplets and contact, with symptoms often resembling a cold but capable of severe illness in infants and people with risk factors.

Public health leaders emphasize responding to real-time disease trends rather than sticking to a fixed calendar, highlighting the need for ongoing surveillance and access to RSV monoclonal antibodies while RSV circulates.

Monoclonal antibodies are a relatively new tool (three seasons available) and are considered game-changers by pediatric health leaders, though some regulators are reviewing RSV shots.

Massachusetts data show Hampden County has the highest RSV-related emergency department visits, followed by the Berkshires, Hampshire, and Franklin counties.