Social distancing, hygiene and face masks are our main weapons to keep the Covid-19 pandemic at bay until a vaccine is found, thoroughly tested and licensed. All three measures are thought to limit the spread of the virus and stop people from contracting the disease. Published in the New England Journal of Medicine, researchers have now suggested that face masks could do even more. Mimicking an early form of vaccination face masks could, they hypothesize, rather than completely stop viral transmission, limit the number of viruses infecting a person and lead to milder or asymptomatic diseases. This way broad immunity (herd immunity) may be reached quicker and safer – without the immense loss of life.
This idea is intriguing, as herd immunity is needed to end this pandemic. Once herd immunity is reached, SARS-CoV-2 can no longer spread as a sufficiently high proportion of individuals are immune to the disease. There is an ongoing discussion about what a sufficiently high proportion is. While most think 60-80% of people need to be immune for the virus to go extinct, a new study using mathematical modeling suggests that 43% may suffice. Unfortunately, we are far from either numbers. Even big cities with huge outbreaks such as New York and Madrid have reportedly reached “only” 19% and 11% immunity, respectively. The cost for these immunity rates were high. Thousands have died and hospital care was pushed to the very limit. The consensus is that only a vaccination can provide a safe way to herd immunity.
Vaccinations train the immune system. They consist either of the whole tvirus – dead or weakened- or a part of the virus (protein or RNA or DNA). In any case the vaccine will not cause disease, while still provoking an immune response and induce long-term memory cells. These memory cells will protect the person from the real virus, if and when he or she encounters it.
The first vaccine was developed by Edward Jenner, who used cowpox to inoculate humans and induce immunity against smallpox. To do so, he injected the fluid from cowpox lesions into humans. Injection of a low viral dose of this related virus only caused weak disease and protected the patients from the deadly smallpox. Same held true when a small dose of virus was transferred from the lesion of a smallpox patient to a health volunteer. And this idea – using low viral loads to induce immunity but not disease – may now be replicated by face masks.
Face masks lower the amount of virus that is expelled into the air from the respiratory system. Getting infected with SARS-CoV-2 when you (and the people around you) are masked, may therefore mean an infection with a lower viral load, which in turn caused a milder disease course. A correlation between viral load and disease burden has been shown in animals, where hamsters infected with a high dose of SARS-CoV-2 developed more severe disease symptoms, quantified by weight loss and CT images, compared to hamsters given a lower dose.
Population wide face masking may therefore increase the number of mild and asymptomatic cases – making Covid-19 less deadly. In fact, Europe is currently seeing a surge of new Covid-19 cases, while the death toll is a lot lower than during the first wave. This may be due to more testing, even mild cases and asymptotic travellers are now being tested and counted in the statistics. An increase in mild and asymptomatic cases may however be linked to the fact that most european countries have imposed strict rules on wearing face masks in public. If true, wearing a mask may help us reach herd immunity while protecting the vulnerable (and everyone else). In the end, I still believe only a vaccine will ensure no deaths and herd immunity – but I rather catch a low virus load and mild disease if I must.