Do masks only protect others? No, it also prevents you from inhaling too many viruses.

*Image by rawpixel.com

We have heard the same message over and over again. Wear masks to protect others. In case one is a carrier, the mask prevents too much spreading of virus particles into the air. But have we forgotten that the reverse is true as well — that masks prevent one from inhaling too many virus particles?

Masks lower the inhaled virus load or inoculum

Monica Gandhi, a professor of medicine at the University of California and director of the UCSF Gladstone Center for AIDS Research, and two other fellow professors published a perspective paper in the Journal of General Internal Medicine on 31 July. The title reads, “Masks Do More Than Protect Others During COVID-19: Reducing the Inoculum of SARS-CoV-2 to Protect the Wearer.”

“However, the second theory — that reducing the inoculum of the virus to which a mask-wearer is exposed will result in milder disease — has received less attention…”

As the title indicates, the professors argued that masks benefit all, including the wearer. The reason has to do with virus inoculum; that is, the amount of virus load or virus particles inhaled. Assuming intact biophysical laws, a lower virus load is easier for the immune system to control. So, even though a mask may not prevent a positive Covid-19 diagnosis, it would diminish the risk of developing severe disease.

“There are two likely reasons for the effectiveness of facial masks: The first — to prevent the spread of viral particles from asymptomatic individuals to others — has received a great deal of attention,” the professors explained. “However, the second theory — that reducing the inoculum of the virus to which a mask-wearer is exposed will result in milder disease — has received less attention…”

Direct evidence from animal studies

Many studies have confirmed the direct causation between virus load and disease severity in animals for all sorts of respiratory viral infections, such as SARS-CoV-2, SARS-1, MERS, influenza A virus (IAV), human parainfluenza virus (HPIV), and infectious hematopoietic necrosis virus (IHNV). In essence, these experiments showed that the more virus particles invading the animals’ respiratory tract, the more severe the disease turned out.

In a hamster study published in May, researchers at the University of Hong Kong showed that 66.7% (10/15) of hamsters contracted Covid-19 through non-contact routes (either aerosols or respiratory droplets). Partitioning their cages with a surgical mask reduced the transmission rate to 16.7%. More importantly, this 16.7% of hamsters also had milder Covid-19 — as evidenced by less tissue damage and expression of virus proteins in the respiratory tract — compared to hamsters whose cages were unprotected.

Indirect evidence from human studies

The paper of Professor Gandhi and colleagues also noted that the rate of symptomless infections was 15% before public mask-wearing was practiced. Now, the rate of symptomless infections has gone up to 40–45%, according to a more recent review and the CDC.

The professors also emphasized that outbreaks in closed settings, such as cruised ships, offer quality insights into infection control. In the Diamond Princess cruise ship outbreak, passengers did not wear masks, and about 82% of infected persons developed Covid-19. In another cruise ship outbreak where passengers wore surgical masks and staffs N95 masks, the prevalence of symptomatic Covid-19 cases was only 19%. That’s about a 4-fold decrease.

Public mask-wearing promotes symptomless cases by several folds. Put it another way; it also means a drastic decline in the risk of severe disease.

Notably, more circumstantial evidence can be derived from local outbreaks:

• In a pediatric dialysis unit in Indiana, 44% (11 out of 25) of healthcare workers contracted Covid-19. Surprisingly, all infected workers developed antibodies against SARS-CoV-2 without showing any symptoms. And these healthcare workers wore masks.
• In an outbreak in a seafood plant in Oregon, only 5% of the 124 infected workers developed symptoms. And these workers received daily masks.
• In another outbreak in the chicken plant in Arkansas, 481 out of 3,748 employees had a positive Covid-19 test, yet 455 (95%) of cases were symptomless. And, again, the employees practiced mask-wearing.
• In Hong Kong, people adopted universal mask-wearing early in the pandemic despite that the WHO and CDC recommended that masks be reserved for healthcare workers only. As a result, Hong Kong has a lower incidence of severe or death cases than in other countries. The same applies to countries that soon started public mask-wearing, such as Japan, Taiwan, Thailand, South Korea, and Singapore.

* Credit to the Facebook group, Curve Crushers: Killing Coronavirus

All of this evidence suggests that public mask-wearing promotes symptomless cases by several folds. Put it another way; it also means a drastic decline in the risk of severe disease.

The case for the silent spread of ‘safe’ infection

So, mask-wearing might have lead to a rise in symptomless cases. There are concerns if this makes it harder to control the pandemic. No symptoms mean that cases are not readily evident, which might be conducive for the silent spreading of SARS-CoV-2.

Do masks only protect others? No, it also prevents one from inhaling too many virus particles.

“Although the asymptomatic infection can be problematic in terms of increasing spread,” Prof. Gandhi and others admitted, “it can also be beneficial.” The professors argued that increased spread also means increased exposure. And since masks reduce the inhaled viral load, infections would not be overly severe. As the professors explained, “Exposing society to SARS-CoV-2 without the unacceptable consequences of severe illness could lead to greater community-level immunity.” Therefore, mask-wearing may be likened to a lower-grade vaccine where it builds some level of immunity.

Short Abstract

Do masks only protect others? No, it also prevents one from inhaling too many virus particles. A lower viral load would make it easier for the immune system to overcome. Many lines of direct animal and indirect human evidence support this proposition. Although masks may not prevent a positive Covid-19 test, it lowers the risk of becoming symptomatic and, consequently, life-threatening Covid-19 complications. Although concerns for silent spreading exist, it can be compensated by the lower risk of severe Covid-19 in mask-wearers, which might also help boost herd immunity.

This article was originally published here.