The drug was 81% effective against RSV hospitalization.
For flu, the sensitivity of the definition was 76% and specificity was 31%; for RSV, those numbers were 71% and 39%, respectively.
Risks rose steeply from 30 days to 1 year for RSV and flu patients.
Compared with controls, nirsevimab was tied to an effectiveness of 62% against all-cause lower respiratory tract infection hospitalizations.
The CDC also provided data on the rise of subclade K among H3N2 flu viruses ahead of holiday gatherings.
Older adults and infants are especially vulnerable to severe RSV, with possible complications of bronchiolitis, pneumonia, and sepsis.
In addition, the emergence of the influenza A H3N2 subclade K virus fueled a record number of flu cases in Australia this year and extended the season, which may have implications for the Northern Hemisphere season.
Researchers identify nearly 5 excess cardiovascular events per 100 patients in the year after diagnosis.
A representative from Sanofi told Reuters that the safety of Beyfortus has been repeatedly shown in over 50 studies.
Just 34% of US adults have gotten a flu shot, 25% have had a COVID vaccine, 8% have received the pneumococcal vaccine, and 6% have been vaccinated against RSV.
