With community transmission of #COVID19 in multiple countries it appears that containment of the virus in China will not happen (this outcome was not unexpected). Emphasis in many places could turn from containment to “mitigation”. What does mitigation mean?
First, to be clear: it’s not either/or, because containment efforts and mitigation efforts encompass a spectrum of activities, are complementary and can occur at the same time.
Still, we can contrast their goals: containment is meant to halt transmission, while mitigation is meant to reduce negative impacts of transmission.
For the U.S., CDC has long had recommendations for how communities can use mitigation to address pandemic influenza. A revision to this guidance came in 2017, incorporating lessons learned from the 2009 H1N1 influenza pandemic. cdc.gov/mmwr/volumes/6…
Not all guidance from pandemic influenza is applicable to #COVID19 because the epidemiology and circumstances differ, but countries face similar challenges with both.
For example, both are highly transmissible, and in both cases we have no specific countermeasures available at first (e.g. vaccines). Containment is difficult if not impossible in both cases.
The 2009 H1N1 pandemic is often remembered as being “mild”, but there was a quite a significant health impact: an estimated 43-89 million people in the US were infected and 12,000 people died between Apr2009-Apr2010.
CDC talks about mitigation in three buckets: 1) individuals behaviors (hand hygiene, staying at home, avoiding ill people); 2) “social distancing” (closing schools and public gatherings, and 3) environmental mitigation (surface cleaning efforts). Let’s focus in 1 and 2.
Encouraging better individual hygiene behaviors is cornerstone of mitigation. Good hand hygiene (wash those hands!), and voluntary home isolation when ill (and even home quarantine when potentially exposed) are recommended.
Many studies show the effectiveness of hand hygiene; one study on H1N1 from Egypt highlighted by CDC showed 47% fewer cases of influenza occurred after twice-daily hand washing and health hygiene instruction was provided in elementary schools.
Studies of the US public during H1N1 found that people actually did change their hygiene behaviors: in one survey 59% of Americans reported washing hands more frequently and 25% said they avoided public places like sporting events, malls, and public transportation.
CDC guidelines also support social distancing in some cases, including school closures, canceling public gatherings, and workplace closures/telework.
During H1N1, CDC recommended communities with confirmed cases consider closing child care facilities and schools. From Aug–Dec 2009, communities in 46 states implemented 812 dismissals (in a single school or all schools in a district), affecting 1,947 schools.
This number of schools represented 0.7% and 3.3% of all urban and rural schools, respectively, in the U.S. Evidence from TX indicated school closures there reduced acute respiratory illness in households with school-age children by 45%–72%.
Interestingly, surveys of parents whose children were affected by school closures found strong support for, and belief in the effectiveness of these measures: 90% of parents agreed with dismissal decisions, and 85% believed dismissals reduced transmission.
Even so, closing schools was disruptive, and a systematic review of US school closures during H1N1 was not able to determine whether the benefits outweighed the cost in this “mild” epidemic, though they did recommend such measures during a “severe” pandemic.
CDC guidelines also note there are practical obstacles to asking people to stay home from school and work: in 2009 a major difficulty was that many people did not have access to paid leave, and therefore had a hard time following guidance.
Another challenge for mitigation in the U.S. is that while CDC can offer recommendations and guidance, implementation of these policies mostly occurs at local district, county, & state levels. This can lead to a patchwork of different mitigation approaches across locations.
A recent publication looked at US local health department decision-making around social distancing during outbreaks, and concluded resources available and actions implemented are inconsistent and unpredictable across the country. …ls-sagepub-com.proxy1.library.jhu.edu/doi/pdf/10.117…
CDC guidance urges flexibility in implementing mitigation measures, and continual re-assessment of their effectiveness as new information comes in. A “targeted, layered” approach that addresses current circumstances is the best practice.
The ultimate goal of such measures is to reduce the intensity of an outbreak, flattening out the epidemic curve and therefore reducing strain on the health system, and on social economic well-being (see this graphic representation). 
