High Dose, Low Dose? Dose Size Matters

There's an excellent article in the NYT today that may help explain the large number of people who, while infected by the SARS2 virus, exhibit no symptoms or only mild symptoms. The article is non-technical but highly informative, with real life implications. It provides concrete guidelines for safe behavior. Without minimizing the dangers of Covid19, it also provides reassurance that there are common sense steps we can take with confidence that those steps will limit the danger we face--like, masking up:

These Coronavirus Exposures Might Be the Most Dangerous 

As with any other poison, viruses are usually deadlier in larger amounts. 

By Joshua D. Rabinowitz and Caroline R. Bartman

Basically, the authors point out that, as with any poison, so to with viruses: The amount of the dose we receive makes a real difference:

As with any other poison, viruses are usually more dangerous in larger amounts. Small initial exposures tend to lead to mild or asymptomatic infections, while larger doses can be lethal.  

From a policy perspective, we need to consider that not all exposures to the coronavirus may be the same. Stepping into an office building that once had someone with the coronavirus in it is not as dangerous as sitting next to that infected person for an hourlong train commute.  

This may seem obvious, but many people are not making this distinction. We need to focus more on preventing high-dose infection.

While the authors don't raise this issue, what they're saying may suggest a fairly obvious explanation for the high degree of variance we're seeing in the severity of illness that Covid19 patients exhibit: from no symptoms at all to death.


We are increasingly hearing from medical personnel that the SARS2 virus is, in most cases, transmitted by touch--from touching an infected person or surface and then touching our faces. We also know that it can be transmitted via the air we breathe, but that appears to be  definitely less common--especially if we maintain a safe distance of a few feet from other persons who may be infected.

This confirms and flows from the initial reports that SARS2, while more transmissible than SARS-Classic, is less transmissible than the flu.

Those considerations lead to practical measures: maintain a safe distance and limit contact, wear gloves and masks when possible in possibly infective situations. If you can limit any dose of virus you receive you'll be doing yourself a big favor. The nonsense we hear that any mask, for example, that doesn't filter 99% of viruses sprayed directly at it is useless is unscientific twaddle. Dose matters. Aim to limit the dose. That's a doable thing:

Because dose matters, medical personnel face an extreme risk, since they deal with the sickest, highest-viral-load patients. We must prioritize protective gear for them.  

For everyone else, the importance of social distancing, mask-wearing and good hygiene is only greater, since these practices not only decrease infectious spread but also tend to decrease dose and thus the lethalness of infections that do occur. While preventing viral spread is a societal good, avoiding high-dose infections is a personal imperative, even for young healthy people.  

At the same time, we need to avoid a panicked overreaction to low-dose exposures. Clothing and food packaging that have been exposed to someone with the virus seem to present a low risk. Healthy people who are together in the grocery store or workplace experience a tolerable risk — so long as they take precautions like wearing surgical masks and spacing themselves out.  

A complete lockdown of society is the most effective way to stop spread of the virus, but it is costly both economically and psychologically. When society eventually reopens, risk-reduction measures like maintaining personal space and practicing proper hand-washing will be essential to reducing high-dose infections. High-risk sites for high-dose exposure, like stadiums and convention venues, should remain shuttered. Risky but essential services like public transportation should be allowed to operate — but people must follow safety measures such as wearing masks, maintaining physical spacing and never commuting with a fever.