How flu viruses spread

A new research study conducted in the US examined individuals from 116 households in who had two positive tests for having flu. The participants or their parents kept a diary regarding symptoms. (1,2)

Highlights of the study include:

• Eleven of the cases tested positive for flu with no symptoms.
• Children under 5 years of age tended to show more symptoms than do older children or adults.
• Children under 5 tend to shed more of the virus and to shed the virus for a longer period of time than did older children or adults.
• People can continue to shed the virus for more than 5 days after symptoms disappear. Post-symptom shedding is highly specific to the individual and, at least at this point, not predictable.

“Shedding” means releasing the virus from their body back into the environment for others to catch.

Functionally, children under 5 appear to be vectors for the flu virus. That poses serious challenges for parents and child care facilities.

A second take-away is that the old rule of thumb about staying home or keeping a child at home for 24 hours after a fever breaks may not work. There’s a reasonable chance they can still infect co-workers and classmates when they return.

Flu is neither trivial or fun. What can happen:

Sinus and ear infections are examples of moderate complications from flu, while pneumonia is a serious flu complication that can result from either flu virus infection alone or from co-infection of flu virus and bacteria. Other possible serious complications triggered by flu can include inflammation of the heart (myocarditis), brain (encephalitis) or muscle tissues (myositis, rhabdomyolysis), and multi-organ failure (for example, respiratory and kidney failure). Flu virus infection of the respiratory tract can trigger an extreme inflammatory response in the body and can lead to sepsis, the body’s life-threatening response to infection. Flu also can make chronic medical problems worse. For example, people with asthma may experience asthma attacks while they have flu, and people with chronic heart disease may experience a worsening of this condition triggered by flu.(3)

“Long flu” and “long Covid” are both real. Most people who get the flu are sick for a few days, recover and return to “normal”. Most but by no means all. Some people develop long term complications and face an increased risk of death. Influenza creates respiratory issues; Covid affects a variety of organs including heart and brain. Readmission to a hospital and death are more likely in the months following infection than during the initial infection.

Long COVID is much more of a health problem than COVID, and long flu is much more of a health problem than the flu.

Ziyad Al-Aly, MD, a clinical epidemiologist at Washington University in St. Louis (2)

Take-away: The flu is problematic for both the elderly and for this with immune system issues. For those people vaccination is a must. For the rest, well, do you really want to be one of the “lucky ones” who gets serious damage? You might want to talk to your doctor.

The map shows the spread of the flu virus January 6-13, 2004.(4)

Sources:

1. Sinead e. Morris et. al., “Influenza virus shedding and symptoms: Dynamics and implications from a multiseason household transmission study”, Procedings of the National Academy of Sciences Nexus, September 2024. Abstract at https://phgkb.cdc.gov/PHGKB/cdcSCFinder.action?Mysubmit=init&action=search&query=39246667&ACSTrackingID=USCDC_520-DM136434&ACSTrackingLabel=Science%20Clips%2C%2016%3A37%20new%20edition%20alert%2C%20September%2016%2C%202024&deliveryName=USCDC_520-DM136434 also available at the National Library of Medicine, https://pubmed.ncbi.nlm.nih.gov/39246667/#full-view-affiliation-2
2. https://medicine.wustl.edu/news/long-flu-has-emerged-as-a-consequence-similar-to-long-covid-19/
3. https://www.cdc.gov/flu/symptoms/symptoms.htm
4. https://www.cdc.gov/flu/weekly/usmap.htm