A British study by Ben Killingley and 31 co-authors recently appeared in pre-print form, where 36 (heroic) healthy young adult volunteers were deliberately exposed to the Covid virus by nasal drops. These volunteers then went into quarantine for 14 days, and logged their symptoms and were subjected to various tests for a total of 28 days.

Of the 36 subjects, only 18 (53%) became infected with the virus, as determined by PCR testing (the gold standard for Covid tests) and by direct counting of viral loads in mucus cells by FFA.

The study found that viral shedding (as estimated by mucus viral loads) begins within two days of exposure and rapidly reaches high levels, then declines. Viable virus is still detectible up to 12 days post-inoculation. This result supports the practice of people quarantining for at least 10 days after they first exhibit symptoms of infection. There were significant higher viral loads in the nose than in the throat,  which supports the practice of wearing masks that cover the nose as well as the mouth.

The cheap, fast, LFA rapid antigen test method (used in home tests) performed fairly well. Because it is less sensitive, it did not it did not yield positive results for infected individuals until an average of four days after infection, or about two days after viral shedding may have begun. But from four days onward, the LFA method was sensitive and reasonably accurate which supports the ongoing use of these quick, cheap tests.

These direct inclusions from the paper are helpful, but not earthshaking. The elephant in the room, which the paper did not seem to directly address, is why nearly half of the people who were exposed did NOT become infected. This raises all kinds of issues about what mechanisms the human body may have to naturally fight off COVID or similar viral infections. Gaining insight on this could lead to breakthroughs in preventing or mitigating this pernicious virus.

An article by Eileen O’Reilly at Axios probes these questions. There is nothing conclusive out there, but four ideas that are under investigation are:

1. Cross-immunity from the four endemic human coronaviruses is one hypothesis. Those other coronaviruses cause many of the colds people catch and could prime B-cell and T-cell response to this new coronavirus in some people.

2. Multiple genetic variations may make someone’s immune system more or less susceptible to the virus.  Some 20 different genes have been identified which affect the likelihood of severe infection, and a genetic predisposition to not getting infected is seen in other diseases where people have one or multiple factors that interfere with the virus binding to cells or being transported within.

3. Mucosal immunity may play an underrecognized role in mounting a defense.

This suggests nasal vaccines might have a chance at stopping a virus before it invades the whole body.

4. Where the virus settled on the human body, how large the particle was, the amount and length of exposure, how good the ventilation was and other environmental circumstances may also play a role.

These considerations support continuing with the usual recommendations of social distancing, wearing facemasks, and ventilating buildings, especially when caseloads are peaking. Also, the doses administered to the volunteers in the study were considered quite small by clinical standards. It was surprising that such a low dose was effective as it was in causing full-blown infections; and the particular strain used in the experiment was not necessarily one of the more recent highly virulent variants. After reading these results,  it is more understandable to me why so many reasonably careful friends and family members of mine (nearly all vaccinated, fortunately) have come down with (presumably) omicron COVID in the past two months. Just a little dab will do ya.