The coronavirus disease (Covid-19) can spread through just breathing and talking, said a high-level US scientific panel on Wednesday, suggesting that the virus that causes the disease is airborne and is spreading more easily and sustainably between people than previously believed.
The scientists said the virus can be stay suspended in air in the ultrafine mist that is produced when people exhale.
“While the current specific research is limited, the results of available studies are consistent with aerosolisation of virus from normal breathing,” said a letter written by Dr Harvey Fineberg, who is chair of the National Academies of Sciences, Engineering, and Medicine’s standing committee of experts to inform the US federal government on critical science and policy issues related to emerging infectious diseases and other public health threats.
“This could explain why the virus is spreading so quickly, and with evidence of asymptomatic spread of the disease, complete social isolation and lockdowns become critical to contain the disease,” said a virologist, requesting anonymity.
Airborne viruses and bacteria, particularly, are more contagious and worrying for highly populated countries like India, where cluster outbreaks have started in congested neighbourhoods, like Dharavi in Mumbai. Around Covid-19, 2,600 cases and 70 deaths have been reported in India so far.
“From what is known, the virus that causes Covid-19 is not as infectious as measles or the tuberculosis bacterium, but more infectious than the seasonal flu,” said Dr Jacob John, professor emeritus and former head of virology at Christian Medical College, Vellore.
Scientists have so far maintained that Sars-Cov2, the virus that causes Covid-19, spreads when infected people cough or sneeze and expel virus in large respiratory droplets that are about 1 mm in diameter. The viral released depends on how infective the person is.
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The most common symptoms of Covid-19 are fever, cough and fatigue, which progresses to difficulty in breathing.
The infection spreads when these droplets are inhaled by people in a radius of two metres, or contaminated surfaces and objects, which people may touch and then infect themselves by touching their mouth, nose, or eyes, according to the World Health Organization (WHO).
But a study in the New England Journal of Medicine forced a rethink when it reported the that virus stays suspended and infective in aerosol droplets that are below 5 microns across for up to 3 hours.
A scientific brief last week from the WHO said aerosol transmission “may be possible in specific circumstances and settings that generate aerosols,” such as when severely ill patients are intubated with a breathing tube for ventilator support, but added that an analysis of more than 75,000 coronavirus cases in China revealed no cases of airborne transmission.
Another recent study from the University of Nebraska Medical Center found viral RNA on hard-to-reach surfaces and air samples more than 2 meters from the patients in isolation rooms, which indicates the virus can spread through aerosols.
“Finding RNA in the environment using PCR-based tests is not a scientific way of measuring transmission as finding nucleic acid (genetic material, which includes DNA and RNA) is not indicative of virus viability. RNA by itself is not transmissible and infective. The outer wall of the virus, which is what it uses to enter human cells, gets destroyed pretty quickly,” said Dr Jacob John.PCR is short for polymerase chain reaction.
If not used properly, personal protective equipment (PPE) could also be a source of airborne contamination, with a pre-print study from China showing the virus can be re-suspended in air when health workers remove their PPE or move around in infected areas.
Several countries are reviewing whether everyone should wear masks in public to reduce transmission. “Of course you need protection, but basic precautions are enough. Everyone is wearing masks, but I still think social distancing and handwashing is what’s needed, unless you are around a person with Covid-19,” said Dr John.
“I’m not going to wear a surgical mask, because clinicians need those. But I have a nice western-style bandana I might wear. Or I have a balaclava. I have some pretty nice options,” Dr Fineberg, former dean of the Harvard School of Public Health, told CNN.