In view of the latest data, the summer has not been any guarantee that the numbers of infections and hospitalizations due to coronavirus will remain low in our country. New cases have been on a steady rise since mid-July and this fall is critical to controlling the epidemic. However, despite this sustained increase in cases of infections in Spain and many other countries, mortality has not (yet) skyrocketed.
There are multiple and varied reasons for this. The main cause behind this phenomenon is that in recent months the capacity to detect coronavirus cases is much greater than in the months of confinement (March-May), in which the peak of the iceberg of the epidemic was barely visible. Now we see a multitude of asymptomatic and mild cases that previously escaped and that gives the apparent feeling of a milder epidemic. In addition, more measures have been taken to minimize the risk of contagion among the elderly and other people at risk. Another factor that influences this trend is that hospitalizations and deaths always appear weeks late with respect to new infections and that medical treatments have improved in these months.
However, multiple researchers and physicians propose an additional hypothesis that could be contributing to the current epidemic showing a kinder side, with proportionally fewer hospitalizations and deaths: the widespread use of masks in the general population.
On September 8 it was published in the medical journal The New England Journal of Medicine (The NEJM) an article which analyzes and raises the following hypothesis: could the use of masks, in addition to reducing the risk of contagion, lessen the severity of the infection and favor that a higher percentage of infections were asymptomatic or mild? Whether the answer is yes or no depends on a key factor that remains unknown: whether the dose of coronavirus a person receives influences not only the chances of infection, but also the severity of the resulting disease. If the dose is important in this matter, using masks could decrease the viral doses to which people are exposed and, in the case of infections, these could be milder or even asymptomatic.
At this time, we do not know what the dose or amount of coronavirus is necessary to become infected, nor do we know if being exposed to a high number of coronaviruses could trigger a more serious infection. Months ago, the position that prevailed is that, once the infection occurs, the dose of coronavirus received did not influence, in most cases, on the severity of COVID-19 or its prognosis. After all, any dose of coronavirus received from other people is negligible compared to the amount of coronavirus (millions and millions of them) that are produced in the human body of the infected person days later. Furthermore, under normal conditions, the general population should not be exposed to huge doses of coronavirus such as can be found in hospital areas with severely affected COVID-19 patients.
Previous studies in which volunteers were inoculated with influenza A viruses indicated that volunteers who were exposed to higher doses they showed no worse symptoms. However, for infections by other types of viruses, it has been observed that giving small doses helps the immune system fight it more effectively and the infection is much milder. This is the principle by which smallpox was inoculated in a controlled way (a technique called variolation), before the vaccine arrived.
However, we do not know if the same result can occur with the SARS-CoV-2 virus and it is not easy to know. It would be unethical to conduct research that purposely exposed humans to different doses of coronavirus to find out. However, there are other types of studies that can clarify and offer us clues on this issue: animal experiments and epidemiological studies. An investigation made with hamsters observed that those who were protected in their cages with a screen formed by the material of the surgical masks not only got less coronavirus than those without this protection, but that asymptomatic cases and with milder symptoms were more frequent.
With regard to epidemiological studies, the authors of The NEJM article point out that there were around 20% asymptomatic cases in the coronavirus epidemic that emerged on the cruise ship. Diamond princess, a place where there was no universal use of masks. A very different figure from 81% of asymptomatic cases that was observed in an Argentine cruise ship in which the passengers had surgical masks and the crew with N95 masks. In any case, these differences could be due to different characteristics of the passengers between the two cruises (age, sex, risk factors …).
On the other hand, in two recent epidemics In food processing plants in the United States, a high proportion of asymptomatic patients (95% of those infected) was also observed. At these plants, all workers had to wear masks every day, and the researchers argue that the use of masks could have contributed to this result.
Although these and other indications are not robust enough to affirm the protective role of masks against serious infections, health authorities are aware of this possibility when it comes to keeping the pandemic under control. Perhaps it is another reason that explains why, despite the increase in cases, countries with widespread use of masks do not observe such a drastic increase in hospitalizations and deaths. This is an important factor that should be further investigated, not only because of the current health crisis, but also because of future pandemics that will appear in the future.