Though previous trials have shown high vaccine effectiveness, most trialed adults were 75 years or older.
Flu activity continues to elevate, and COVID-19 markers are also starting to rise from very low levels.
Disease burden, hospitalization rates have stayed the same from 2017 to 2024.
The FDA says the hold is related to concerns about safety findings from a now-paused clinical trial of two RSV vaccine candidates in infants.
In its weekly respiratory illness snapshot, the CDC upgraded the level from low to moderate.
There were 24 cases of RSV infection through day 151 in the nirsevimab arm and 54 in the placebo arm.
But the risk of bacterial infections in COVID-19 patients was substantially elevated after 48 hours compared with the other viruses.
The authors add that catch-up nirsevimab administration is a powerful tool for reducing primary care burden during RSV season.
In its annual National Influenza Vaccination Week messaging the CDC said there's still time to benefit from getting a flu shot this season.
The number of doses of nirsevimab needed to prevent 1 RSV hospitalization is estimated at 128.
