Face Facts

Stanford, Calif.

DESPITE all the attention given to anthrax and smallpox and potential weapons of mass destruction, pandemic influenza is probably the world’s most serious near-term public health threat. If a strain similar in effect to the 1918 Spanish flu (which killed tens of millions of people worldwide) emerges in the next several years, it is highly likely that an effective vaccine will not be available during the pandemic’s first wave, that we won’t have enough antiviral drugs for large-scale prophylactic use, and that hospitals will be too overwhelmed to treat most cases.

Consequently, as in 1918, we will need to combine medical efforts with voluntary and forced social changes — closing schools and churches, canceling public gatherings, keeping workers at home — to hinder the flu’s spread. Our government must draw up a plan for educating the public about effective nonpharmaceutical interventions like hand washing and face protection like masks.

A prerequisite for doing so is determining the biggest culprit in spreading influenza: droplet transmission, in which an infected person sneezes or coughs directly into the mouth, nose or eyes of someone who is susceptible); contact transmission, in which virus is transferred via hands either directly, say, through a handshake, or indirectly through an object like a doorknob; and aerosol transmission, in which evaporated virus-containing particles are inhaled.

Remarkably, this issue has not been resolved: the Department of Health and Human Services’ Pandemic Influenza Plan states that “the relative clinical importance of each of these modes of transmission is not known.” As a result, the government enthusiastically endorses frequent hand washing — which would reduce contact transmission, and costs nothing — but remains noncommittal about face protection. While the government says that it might be beneficial, it doesn’t make respirators or masks available. Yet face protection would guard against aerosol and droplet transmission, and even reduce contact transmission by making it difficult to place fingers into one’s mouth or nose.

A Stanford graduate student, Michael Atkinson, and I recently performed a detailed study of the routes of transmission, using data on influenza and on rhinovirus, which causes the common cold. Our findings suggest that the dominant mode of transmission for influenza is aerosol — implying that hand washing will make little difference. This is consistent with the views of leading researchers several decades ago, views that have somehow been forgotten by the public health community.

We found that ventilation, like placing a fan in an open window, and humidifiers (most influenza strains survive in the air for much less time when the humidity is raised to about 65 percent) can reduce transmission slightly. Sleeping in separate bedrooms (and working in separate offices) can help even more.

But the single most effective intervention is face protection. And because roughly one-third of influenza transmissions occur before an infected person exhibits symptoms, these precautions should be taken whenever people are in the same room throughout the pandemic period.

There are two kinds of face protection: N95 respirators, as worn by construction workers, for instance, and surgical masks of the sort worn by dental hygienists. (The respirators cost roughly a dollar apiece, the surgical masks 10 cents.) Their efficacy in preventing aerosol transmission depends on three factors: the extent to which the face filter prevents virus particles from passing through, how tightly the device fits and — most important — how long people can be coerced into wearing them.

To our surprise, we found that the filters in surgical masks, although not as good as the filters in N95 respirators, are still quite effective. And although a surgical mask fits much more loosely and allows more leakage, it’s also more comfortable — and therefore likely to be effective because it’s used more. Wearing nylon hosiery over a surgical mask essentially eliminates the face leakage, making this combination a practical, albeit macabre, alternative. The less comfortable N95 respirators would probably result in lower compliance.

The government doesn’t stockpile masks and respirators, and the manufacturers aren’t able to produce a huge number of them quickly. But the way forward seems clear: the government needs to build up a supply of respirators and masks just as it does with vaccines and antivirals. It should first hire a whiz-bang design company to create, within one month, a surgical mask that comfortably adheres to the face, and then decide on the appropriate mix of respirators and masks. Next, it needs to sign contracts with manufacturers to stockpile masks and respirators, relieving the manufacturers of liability issues.

Although there is very little technological risk involved (masks and respirators are easier to make and safer to use than vaccines), several issues need to be ironed out. First, the effectiveness of N95 respirators and masks varies widely. The government needs to educate the public (the brands are anonymous in the published studies) and should stockpile only the most effective brands.

Also, if respirators and masks are discarded daily, as they are in many hospitals, the national demand during a three-month pandemic could be 10 to 20 billion, and the cost for respirators for a family of four several hundred dollars. Such waste isn’t necessary. The virus does not survive longer than a few hours on the material used for masks and respirators, so they should be re-used until they disintegrate.

The government and the public health community must switch mindsets, from the current perspective of protecting workers paid to do a dangerous job everyday, to that of providing citizens with the tools to best protect themselves during a pandemic.

It may take 18 months to build a stockpile of respirators and masks, so there is no time to lose. The American people’s faith in their government will be seriously undermined if, along with larger measures like school closings, it cannot provide effective face protection for its citizens during a deadly pandemic. Masks and respirators may be our main lines of defense during a pandemic.