The WHO NPI Guidance : Personal Protection

Credit WHO

#14,500

On Friday, in WHO Guidance: Non-pharmaceutical Public Health Measures for Mitigating the Risk and Impact of Epidemic and Pandemic Influenza, we took our first look at the World Health Organization's recently released 91-page NPI Guidance document.

NPIs - or Non-Pharmaceutical Interventions - are those actions (apart from taking vaccines & antivirals) that individuals and communities can do to help slow the spread of an infectious disease.

They won't stop a pandemic, but they can help reduce its impact, by `flattening the epi curve '. This will make for longer, but more manageable, pandemic waves.

The new WHO guidance divides NPIs into four broad categories; Personal Protection, Environmental Measures, Social Distancing Measures & Travel Related Measures. 

Today we'll be looking at the WHO personal protection NPI recommendations for hand hygiene, respiratory etiquette, and the use of (surgical) face masks. 

But first we have to look at the issue of pandemic severity.

The difference (in severity) between the 2009 and 1918 pandemic was several orders of magnitude. Basically, no two pandemics are alike, and a MERS-CoV pandemic would likely play out far different from an influenza pandemic.

Early estimates of the severity of the emerging H1N1 virus in 2009 proved overly pessimistic, leading some cringe worthy headlines (see UK Told To Brace For Up To 63K Swine Flu Deaths).

In 2017 both the WHO (PISA) and the CDC (PSAF) released updated Pandemic influenza severity assessment frameworks, which - using data on transmissibility, clinical severity, and impact -  help determine a pandemic's current severity (which may change over time).

WHO PISA Determinants Of Pandemic Severity

The goal is to designate pandemic severity as either:

• No activity or below seasonal thresholds 

    * Low 

• Moderate

• High

• or Extraordinary

Things are never that simple, and no one designation will apply globally. What might be a low or moderate severity pandemic in Northern Europe could be a high (or even Extraordinary) severity pandemic in India or Asia.

The WHO's NPI guidance uses their calculated (local) pandemic severity assessment to trigger various levels of NPI recommendations (see chart below).

Some recommendations are universal, appropriate for any level of severity, while some are only issued for more severe pandemic impacts.    

Recommendations are based on scientific evidence (or at least, plausibility) of benefit, balanced by cost and practicality, and any potential harm they may cause. 

In many cases, the scientific evidence for their use is limited, but they fall into the `chicken soup' - it couldn't hurt - category.  Frequent handwashing and respiratory etiquette (covering coughs, sneezes, etc.) are good examples.

They ought to reduce transmission, and are relatively cheap and easy to implement, but their effectiveness in reducing transmission during a pandemic is largely unproven.

Regardless of the strength or quality of the evidence, both of these measures make sense - have little or no downside - and are recommended for all pandemic (and epidemic) severity levels.

The issue of wearing surgical face masks by the general public is somewhat more complicated (and contentious). And here, the WHO divides mask usage into two types:

• Wearing a surgical mask by a symptomatic patient to protect others.

• Wearing a surgical mask by someone uninfected to protect the wearer.

We've looked at the conflicting data on the effectiveness of surgical masks many times over the years (see here, here, and here), and there is little consensus on their merit in protecting the wearer.

The WHO sums up their face mask recommendations, reserving public wearing of face masks by asymptomatic persons to high severity pandemics, while supporting the wearing of surgical masks by symptomatic cases in any scenario.

These are, of course, just recommendations. 

In many places around the world - but most particularly in Asia - many people routinely wear face masks in public during flu season.  As long as masks are available (a supply which is far from assured), it is unlikely these people will hold off doing so during a low or moderate severity pandemic.

Our Strategic National Stockpile contains more than 100 million N95 and surgical masks (see Caught With Our Masks Down), but more than 10 years ago the HHS estimated the nation would need 30 billion masks (27 billion surgical, 5 Billion N95) to deal with a major pandemic (see Time Magazine A New Pandemic Fear: A Shortage of Surgical Masks).

The WHO also weighs in on the use of homemade, cloth, or reusable masks: 

Reusable cloth face masks are not recommended. Medical face masks are generally not reusable, and an adequate supply would be essential if the use of face masks was recommended. If worn by a symptomatic case, that person might require multiple masks per day for multiple days of illness.

Again, while not recommended, I can see a lot of people resorting to homemade, or reusable masks when the supply of disposable masks runs out. (see 2006 EID Journal letter  Simple Respiratory Mask). For many people around the world, disposable masks won't even be an option. It will be home brew, or nothing.

The bottom line, if you want disposable face masks for the next pandemic, you'd probably better buy them now. Once a pandemic starts, their availability will quickly dwindle.

NPIs won't stop a pandemic, or guarantee you won't get sick.  At best, they can slow the spread of a virus, and reduce the pandemic's impact on society.

Our hospitals are more likely to be able to cope with 100,000 flu cases a week, than with a million. Our infrastructure is more likely to remain operating with 15% of the workforce out sick (or caring for loved ones) than with 50%.  

Despite less-than-robust evidence for their effectiveness, anything we can do to slow the spread of a pandemic - without causing additional harm - could pay enormous dividends.

We'll revisit this WHO guidance document - and look next at social distancing recommendations - in an upcoming blog post.