Federal data shows that positivity rates of RSV are significantly higher than this time last year.

As a result, some states have extended the window for immunizations. Shots for infants and toddlers will now be available through the end of April.

RSV typically follows a fall to spring pattern and immunizations are normally recommended through the end of March.

The shifting dates means providers can offer vaccines for a longer period of time.

Experts say that is critical because RSV remains the leading cause of infant hospitalization.

Although doctor don't know why the virus has struck around, they say continued access to immunization could make a real difference.