Researchers say people staying indoors during the 2009 swine flu outbreak in Mexico City reduced virus transmission, indicating social distancing policies may be effective.
In early January, the Centers for Disease Control and Prevention (CDC) revealed that the current flu season had already reached the threshold for epidemic status, with a significant increase in flu activity across the US in space of 1 week and 15 child deaths from the virus so far.
In their report released last week, the CDC revealed that the high flu activity is likely down to low vaccine effectiveness; this season's flu vaccine only reduces a person's risk of visiting a doctor due to the virus by 23%.
The organization says this is primarily because around 70% of this year's H3N2 viruses - the predominant influenza viruses - are "drift variants," which are those that possess antigenic or genetic changes that make them different from the virus included in this season's flu vaccine, meaning the vaccine's effectiveness is reduced.
Because of the vaccine's low performance, the CDC urge all individuals at high risk of flu-related complications - such as young children and the elderly - to seek additional prevention and treatment measures against influenza.
In this latest study, lead author Michael Springborn, of the University of California-Davis, and his team state that non-pharmaceutical interventions (NPIs) - prevention or treatment strategies that do not involve the use of medication - may be highly effective for staving off flu in an epidemic.
In particular, the researchers say "social distancing" - staying indoors and avoiding social interaction with other people - may be key to reducing the spread of infection.
Without social distancing controls, flu transmission is higher
To reach their conclusion, Springborn and his team assessed data on home television viewing during the 2009 swine flu outbreak in Mexico City. According to Springborn, television viewing data "highly correlates with time spent in the home," so it is a good measure of social interaction.
- Get an annual flu vaccine. The CDC recommend the flu vaccine to everyone aged 6 months and older
- Take everyday preventive actions to stop the spread of germs, such as washing your hands and covering your nose and mouth with a tissue when you cough and sneeze
- Take flu antiviral drugs if prescribed by your doctor; they can make the illness milder and reduce the amount of time you are sick.
In an attempt to contain the outbreak, caused by the A/H1N1 virus, the Mexican government adopted social distancing measures, which involved school, shop, museum and theater closures, as well as ordering people to stop kissing and shaking hands.
Using the television viewing data, the team assessed the effectiveness of social distancing controls in reducing the spread of flu.
According to the researchers, such controls appeared to be a "key factor in containing the initial wave" of swine flu in Mexico City. The team estimated that if these social distancing controls were not adopted, then the rate of flu transmission would have been much higher.
However, Springborn says the team identified a "rebound effect," meaning social distancing controls were effective at the start of the flu outbreak, but people soon started to spend less time in their homes.
"This suggests that efforts to utilize social distancing to mitigate disease spread may have a limited window of efficacy, i.e., before pent up-demand for activities outside the home takes precedence," he adds.
The team found that people of a higher socioeconomic status and children were most likely to adhere to the social distancing controls, as indicated by the increased amount of time they spend watching TV during the flu outbreak.
They explain that this may be because people with a lower socioeconomic status are more likely to be subject to factors that make staying indoors challenging, such as less flexibility with working hours. "If this hypothesis were tested and verified, it would suggest the potential for targeting of social distancing policies to facilitate self-protective measures for low socioeconomic level individuals," say the researchers.
Overall, the researchers say their findings show that responses to social distancing controls during flu outbreaks "clearly affect the course of disease." They conclude:
"Results suggest that A/H1N1 had an innate transmission potential greater than previously thought but this was masked by behavioral responses. Observed differences in behavioral response across demographic groups indicate a potential benefit from targeting social distancing outreach efforts."
While social distancing controls may reduce the spread of flu, the researchers note that other factors such as hand washing and wearing face masks are also effective.