Most people with the flu stop isolating and return to socializing with others while they are still likely contagious, a new study by the CDC shows, increasing the risk of spreading the virus to others.
Most people with the flu shed most of the viral RNA through their noses an average of four days after symptoms begin — but most people who self-isolate end their isolation around that time, according to the study published Sept. 10 in the American Journal of Epidemiology.
“Most people did not completely isolate themselves from the community or other members of their household for the duration of their symptoms, but many of them did so for at least part of the time they were sick,” said lead author Elizabeth White, an epidemiologist in the CDC’s influenza division.
According to the study, only 5.5% of people isolate themselves from the community for the entire recommended isolation period, and less than 1% isolate themselves from other household members for the entire period.
About 80% of people isolate themselves from the community for some time (for a median duration of four days), but only 21% isolate themselves from other household members (for a median duration of two days), according to the analysis. Researchers recognized that isolating themselves from family members may not be practical for people who need to care for their children when they or their children are sick.
Flu season usually begins in October and peaks from December to February. In California, 34 people have died from the flu so far this season, according to state data, with San Francisco reporting its first flu-related death of the season last week. Public health officials are urging everyone over the age of 6 months to get vaccinated before the winter break.
The CDC study findings highlight the importance of post-isolation precautions such as additional hand washing, masking, improving indoor air quality, and cleaning frequently touched surfaces, which can help reduce the risk of spread if people resume activities with others while continuing to shed the virus. Viral shedding is an indicator of contagiousness, but not an exact measure of it.
The length of time people should self-isolate when they have the flu does not depend on how many days they have been sick. Instead, the CDC’s guidance is symptom-based: People can end isolation when their symptoms have improved for 24 hours, which includes not having to take fever-reducing medications for 24 hours. After that, they should take other post-isolation precautions for five days, such as increased hand washing, masking, cleaning frequently touched surfaces and improving indoor air quality, according to CDC guidelines.
The study looked at how well CDC guidelines aligned on flu virus shedding and isolation, and the results supported the agency’s guidelines that people should stay home and away from others until their symptoms improve for 24 hours, White said.
The study included approximately 1,300 adults, adolescents and children with influenza in Missouri, New York and Tennessee over two flu seasons, 2023-24 and 2024-25. Most participants, 56%, were children, and 70% of participants had not received their annual flu vaccine. The researchers took daily nasal swabs and asked participants about their symptoms.
White said the takeaway for the public is to try to stay home as much as possible when sick.
“This can help reduce the spread of flu in the community,” she said.
Gn Health
