HOW DOES THE VIRUS SPREAD?

More on Covid-19

WHAT’S THE IMPACT OF EXPOSURE TO THE VIRUS?

Exposure vs Risk of infection

Exposure vs Severity of illness

WHY MASKS ARE CRITICAL IN REDUCING VIRAL LOAD

Non-fitted masks vs Covid-19

Graphics: Sajeev Kumarapuram

Source: Nature Medicine, BMJ, Risk Analysis, New Yorker, Ars Technica

After months of insisting that masks aren’t necessary unless you’re unwell, health agencies across the globe are now encouraging mask-wearing for everyone. And the move appears to be backed by research that suggests masks, even homemade face covers, can be effective in protecting against Covid-19. But to understand why masks are critical, we must understand how the virus spreads and what different levels of exposure to the virus can mean.The primary way the virus spreads is through respiratory droplets. A cough or sneeze can send respiratory droplets six feet into the air but they are relatively heavy and fall to the ground before getting further.But the virus can spread through aerosol transmission, a process by which respiratory droplets are turned into very small and light particles, less than 5 micrometers in diameter, that can hang in the air for longer. Aerosol transmission is not the primary mode of transmission though.Currently, the coronavirus is being measured as a binary phenomenon — people are either infected or uninfected. But it’s important to measure nuances of the virus on an individual basis Pulitzer prize-winning physician Siddhartha Mukherjee, in a New Yorker article, says there are some questions researchers must answer to understand if preventive measures and treatments are effective:- Is the risk of infection higher if one is exposed to higher doses of the virus?- Does a greater exposure to the virus result in greater severity of illness?Here’s what researchers know so far:- Several studies have found that exposure to larger amounts of some viruses increases the chances of an infection- But it also depends on individual specific factors, like “peak viremia” and “set point”. Peak viremia is the highest point the virus count reaches after an infection and set point is the level to which the virus count settles after reaching its peak- An HIV study showed that people with a higher peak viremia were least able to fight the virus and those with higher set points got sicker faster. Conversely, the immune system may be better able to cope with an infection if the viral load is lower than the peak viremia and set pointData suggest coronavirus poses a greater threat for older people and those with underlying conditions. But several deaths of young healthcare workers have raised questions about the relationship between the extent of viral exposure and the severity of illness.- In Wuhan and Italy, data show that while medical workers don’t have a higher fatality rate, they suffer disproportionately from severe forms of illness. They are also getting exposed to the highest quantities of the virus- One study published in Lancet showed that those suffering more severe forms of Covid-19 had 60 times higher viral loads in their nasal swabs than those with milder forms of the diseaseResearch on the effects of high levels of exposure to the virus suggests protective equipment can be critical, not just for medical workers, but for anyone venturing outdoors and interacting with others during the lockdown. But how effective are masks at reducing exposure to the virus? While there have been no large, high-quality studies on masks, here’s what some of the research conducted so far shows:A study published in Nature on April 3 showed that a non-fitted mask, what most of the public will likely have, can block up to 100% of coronavirus droplets and aerosols. Droplet and aerosol particle counts were significantly lower in those who wore masks than those who didn’t. However, this limited study included only 17 people with coronavirus, 96 with other viruses.