Most people with flu have no symptoms
Less than 25 percent of the population infected with seasonal and pandemic flu—or approximately 1 in 5 people—demonstrate any symptoms, according to a new study.
Scientists from University College London in the U.K. began conducting what is called the Flu Watch study in 2006, comparing the severity of seasonal flu and the 2009 H1N1 influenza pandemic in England over five years. They analyzed data on flu infection incidence, the percentage of people who were infected and showed symptoms and the percentage of people who showed symptoms that led to medical attention. In order to identify incidences of infection, researchers took blood samples from participants before and after each flu season in addition to contacting participants on a weekly basis to identify cases of cough, cold, sore throat and any “flu-like illness.” Participants who reported any symptoms were then tested for viruses.
The results of the study, published in The Lancet Respiratory Medicine journal, showed that 18 percent of the community participants were infected with influenza each winter season. Twenty-three percent of those infected showed no symptoms, and 17 percent of those who tested positive for influenza sought medical attention.
Researchers said that the study’s findings are significant in that they highlight the prevalence of infection and illness in the community and how much it can be underestimated. They expressed concern that people carrying even minor forms of infections may contribute to the transmission of disease. Researchers said that their findings show that more preparation for both mild and severe pandemics is needed, as well as the need for additional community studies to help inform effective responses to influenza outbreaks.