As you might imagine, the volume of coronavirus related research has become staggering. I am trying to sort through and identify a few papers to summarize that might have particular relevance to decision-making around strategies to slow spread.
Several studies have suggested that tuberculosis vaccination may have a protective effect against coronavirus. A new paper further examines this question, noting that some prior studies have found that the vaccine may limit infection by other agents. This paper finds at least a correlation between countries with active tuberculosis vaccination and reduced coronavirus death rates. It suggests the mechanism may be something referred to as “trained immunity”. This seems to be a line of inquiry worth following up on. It would likely be fairly easy in the US to ascertain whether people who have been vaccinated for tuberculosis are less susceptible to coronavirus. I am a little dubious because all health care workers typically have to have a tuberculosis vaccination, yet they are clearly getting infected and even dying from coronavirus. (Medrxiv Paper)
What about mask-wearing? Can it really have a substantial effect in deterring infection spread? Depending on its quality, a mask may prevent both inhalation of virus particles and, for an infected individual, expulsion of such particles. Homemade masks in particular probably have limited efficacy and may actually become a breeding ground for infectious agents. But a proper mask can limit transmission in either direction, although it is not a guarantee against either breathing in or out virus particles. A new paper suggests that wearing masks can help keep transmission rates at a lower level. (Medrxiv Paper) The authors modeled the effect of using a mask, making certain assumptions about how much transmission would be affected. They found that the most benefit occurred at relatively low background transmission rates, with a lesser effect when transmissibility was high.
And as researchers continue to struggle to understand even the basic physics of virus transmission, a new paper looks at what happens when people exhale. (NEJM Article) The authors found that when people speak they generate droplets of various sizes and those droplets can carry infectious agents. Some larger droplets fall quickly and can contaminate whatever surface they fall on. Some smaller ones can evaporate but leave a residual nucleus that can remain airborne as an aerosol for some time. Placing a damp cloth over the mouth while speaking decreased droplet spread. There probably isn’t any question at this point that the virus can be spread by air and we are starting to get a better sense of the mechanics and quantification of that spread.