New CDC guidelines on flu pandemic measures reflect 2009 lessons

New federal guidelines on using nonpharmaceutical measures to fight influenza pandemics reflect lessons learned during the 2009 H1N1 pandemic, with changes that include a new framework for gauging the severity of the threat in the early stages.

The guidelines, covering the use of such steps as home quarantine, face masks, school closings, and social distancing, were issued Apr 21 by the Centers for Disease Control and Prevention (CDC). They replace guidelines issued in 2007 and represent an effort to improve planning and decision-making on when to use nonpharmaceutical interventions (NPIs).

The guidance notes several lessons of the 2009 pandemic:

  • The pandemic virus emerged in North America, not overseas as expected from past pandemics, which meant there was less time to prepare for it.
  • In the early stages of a pandemic, its severity can be overestimated because the most severe cases are the ones most likely to be reported.
  • School-related NPIs were acceptable to most parents.
  • The pandemic was moderate overall, but it hit children, young adults, and pregnant women harder than older adults.
  • It took 6 months to make a vaccine available and 8 months to produce it in large quantities.

With the new guidance, the CDC offers a new "Pandemic Severity Assessment Framework" in an effort to address the problem of judging pandemic severity in the early stages. The framework uses eight measures of transmissibility and five measures of clinical severity to provide a more comprehensive assessment of a pandemic.

An emerging pandemic would be placed in one of four assessment quadrants. As an example, a pandemic could be categorize as having low to moderate transmissibility with moderate to high clinical severity. The quadrants replace the previous "Pandemic Severity Index," a 5-point scale that was similar to the severity scale used for hurricanes and was based strictly on the case-fatality ratio of the new virus. Each assessment quadrant is linked with a "prepandemic planning scenario" for NPIs.

Using this framework, the CDC aims to do a broad, preliminary assessment in the first 3 to 4 weeks after emergence of a new virus, and to follow up with a more refined assessment that may take 4 to 8 weeks. The assessments will be used to guide decisions about NPIs.

The new guidance includes the following information about the CDC's likely advice on the use of specific NPIs in a pandemic:

  • The CDC may recommend voluntary home quarantine for exposed household members of flu patients for up to 3 days.
  • The agency may recommend use of face masks as a "source control measure" for flu patients in crowded or close-contact settings during severe or extreme pandemics.
  • Well persons will not be advised to use face masks except in a few scenarios, such as pregnant women or other vulnerable people in crowded settings or people caring for patients at home.
  • The CDC may recommend preemptive school closures in severe or extreme pandemics, but in moderate pandemics the decision will be left to local authorities.
  • The agency may recommend social distancing steps (for example, that people keep at least 3 feet away from each other) during severe or extreme pandemics.
  • Environmental cleaning is recommended in all settings to eliminate flu viruses on frequently touched surfaces.

The new guidance updates NPI planning guides for families, schools, churches, and workplaces, and it adds guides for people in such occupations as event planning and public health communications.

CDC. Community Mitigation Guidelines to Prevent Pandemic Influenza—United States, 2017. MMWR 2017 Apr 21;66(1):1-34 [Full text]

See also:

Feb 1, 2007, CIDRAP News story on CDC's 2007 NPI recommendations

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