By now, we know that one of the only ways the world can return to normal (whatever that may look like) is through the development of a coronavirus vaccine. And it's not an easy journey. Just last week, the trials at Oxford University were temporarily halted after a participant in the UK had an averse reaction.
But as the world waits for a vaccine with bated breath, some scientists are floating another slightly more provocative idea; that mandatory face mask wearing could be leading to wide-spread immunity.
The research, which was published last week in the New England Journal of Medicine, advances the unproven but promising theory that universal face mask wearing might be helping to reduce the severity of the virus and ensuring that a greater proportion of new infections are asymptomatic.
Although the theory is still in its very early stages, Dr Bharat Pankhania, an infectious disease specialist from the University of Exeter Medical School, says that he finds it “very promising.”
“Masks are not 100 per cent protective, but they may prevent you from getting a large infecting dose,” says Dr Pankhania. “They may expose you to a small amount of virus, which doesn’t give you an illness but does mean that you encounter it.”
It’s this “regular small dose exposure” that eventually leads your body to recognise the coronavirus proteins, and start producing antibodies to fight them off. “That way, you are making antibodies by having sub-clinical infections without getting a large infecting dose in one go which kills you,” adds Dr Pankhania.
If the theory is true, universal mask-wearing would cause immunity to spread through the population through what Dr Pankhania calls “subclinical infections” that show no signs or symptoms.
This theory isn't entirely new. It's actually based on the age-old concept of variolation; the deliberate exposure to a pathogen to generate a protective immune response. It was first tried in response to the smallpox vaccine, but quickly fell out of favour due to its riskiness.
Although variolation – otherwise known as innoculation – isn't identical to a vaccine, Dr Pankhania says its "very similar."
"A vaccine is introducing you to the protein of that virus which it then makes antibodies against. In this case, what it’s doing is giving you a sub infecting dose, but conditioning your immune system to recognise it at the same time,” says Dr Pankhania.
The theory rests on the idea that someone's viral load – the amount of virus they're exposed to at the start of an infection – determines the severity of their illness. The idea became widespread in March after people noticed that key workers who were being exposed to higher doses of Covid-19 – such as bus drivers, nurses and doctors – were more likely to develop severe strains of the virus. Since then, the evidence for viral load has been mounting. A large study published in the Lancet last month found that “viral load at diagnosis” was an “independent predictor of mortality” in hospital patients.
This doesn’t mean that donning a mask will automatically inoculate everyone against the virus though. Experts are in agreement that prevention strategies like frequent hand-washing, social distancing and avoiding crowds remain the most important measures for people to take in stopping the spread of the virus.
Plus, the link between dose and disease is tricky to prove. “I would be interested to look at a country where mask-wearing is the norm, such as East Asia, and see if they have higher levels of antibodies amongst the population,” says Dr Pankhania. Although no study of this kind has been done yet, there is a small body of evidence that suggests a link between dose and disease. Earlier this year, a team of researchers in China found that hamsters housed behind a barrier made of surgical masks were less likely to get infected by the coronavirus. And those who did contract the virus became less sick than other animals without masks to protect them.
A few observations in humans seem to support this trend too. According to a report published by the Centers for Disease Control and Prevention, vigilant mask wearing might have spared nearly 139 people from catching coronavirus at a hair salon in the US. Meanwhile, researchers have uncovered largely silent, symptomless outbreaks in venues from cruise ships to food processing plants, all full of mostly masked people.
A further problem lies in the fact that we don't know exactly how much infectious dose it takes to make someone sick with the virus, says Dr Pankhania. Even if scientists did agree on an average amount, it’s likely that factors such as weight, genetics and a person's immune system can all influence how the virus enters the body.
Although he agrees we should err on the side of caution, Dr Pankhania does think the theory "shouldn't be discounted."
"If anything, it's more of a reason to wear a mask," he adds.
As research persists, scientists are also starting to discover that our immune response to Covid-19 is complex, with the full picture likely to extend beyond antibodies. Recent studies have shown that T-cells – which are part two of a three-phase response to infection – play an important part in the immune response of patients with Covid-19.
Dr Monica Gandhi, an infectious disease physician at the University of California, San Francisco, and one of the paper’s authors, has stressed that the commentary has its limitations and should not be construed as anything other than a theory.
“To test the variolation hypothesis, we will need more studies comparing the strength and durability of SARS-CoV-2–specific T-cell immunity between people with asymptomatic infection and those with symptomatic infection, as well as a demonstration of the natural slowing of SARS-CoV-2 spread in areas with a high proportion of asymptomatic infections,” she told the Sunday Telegraph.