A new article in the Journal of the American Medical Association suggests that social distancing guidelines are based on an outdated understanding of potential transmission mechanisms from infected persons. (JAMA Article) This short article is somewhat technical, but here are some quotes and summaries that may help you understand its meaning. The authors note that “the current understanding of routes of host-to-host transmission in respiratory infectious diseases are predicated on a model of disease transmission developed in the 1930s.” A technical discussion related to droplet sizes in people’s exhalations ensues.
The researchers then discuss more recent research characterizing the makeup of exhalations. They describe exhalations as including a turbulent “puff” cloud that enables droplets, which contain whatever infectious agents are present, to persist for much longer than previously believed and therefore to mix over much longer distances. The droplets could last for minutes and travel as far as 23 to 27 feet. Along the path, various factors would account for rates of evaporation and settling of droplets of various sizes. Droplets that settle along the path contaminate surfaces that they land on. Coronavirus can apparently survive for some time on certain surfaces. Droplets that evaporate become residues or nuclei that can remain suspended in the air for hours and enter artificial or natural air flow systems, where obviously, they have the potential to infect many more persons.
The finding in China of virus particles in coronavirus patients’ rooms’ ventilation systems supports the results of this research. There is more work to be done but if these findings are accurate, they have implications for transmission theories as well as for the design of protective measures and gear for health care workers and first responders. What I take from the study is that an infected person, and remember that probably at least half of the infected are not symptomatic, is walking around constantly exhaling a large and fast moving cloud of droplets which can settle in the near term on various surfaces, but can also produce residues that last and travel far longer.
The study wasn’t specific to coronavirus but there is no reason why the same bio-physics wouldn’t apply. And if the transmission mechanics outlined in the study do apply to coronavirus, coupled with emerging research regarding how long the virus may be able to survive on various surfaces or in various environments, we may have some better explanation for how some people appear to be getting infected without an obvious transmission chain.
I have been saying for some time now that we need to accept the fact that this virus has been with us longer than we think and has spread and become more omnipresent than we have accepted. The World Health Organization recommends a three foot distance between persons and the CDC a 6 foot one, which is far less distance than the new research suggests would be adequate. This means that social distancing, unless we really are going to lock everyone up and hope that no one’s home has any coronavirus in it, is largely futile. We should consider ourselves very fortunate that, for whatever reason, and it would behoove us to figure out that reason, the virus infects potentially only 10% to 20% of the population and the infection rates are very skewed to the older age cohorts.
This also means that unless and until a seasonal effect (and most scientists are suggesting that effect, if it comes, won’t arrive until July or August) comes into being that limits the virus’ spread, we would have to maintain even more aggressive lockdowns. We simply can’t sustain that, economically or socially. It is asking too much of people, of businesses, of governments. There are not resources to support that strategy. The extreme mitigation measures have to stop and they have to stop now, since they can’t be maintained for that length of time and as I never tire of pointing out, they are really just delaying the inevitable.
So we need a new strategy and we need to stop the futile destruction of the economy in largely pointless efforts to reduce spread. The strategy that would make more sense is to focus on segregating the high risk groups. Keep them as isolated as possible and make sure that any contacts are as safe as possible. We may need even more aggressive disinfecting processes for older people’s homes and those of other vulnerable groups. But let the bulk of the population return to work and normal activities, while maintaining good hygiene, some social distancing (although probably not of much value) and quarantines if you are infected or have reason to believe you might be.