Bengaluru/New Delhi: An unusual wooden paddle with a nail-studded leather face at the Smithsonian Institution, US, is a relic from 1899, when authorities in Alabama used it to perforate mail, which was then fumigated with sulphur as a precaution against yellow fever.
A year later, researchers discovered that the disease was spread by a mosquito-borne virus — the exercise of fumigating mail was, thus, futile.
A similar consensus is now evolving regarding Covid-19, with multiple scientists suggesting that the emphasis on contact transmission may be misplaced.
Since the start of the pandemic, prevention guidelines from health agencies around the world have stressed the need to disinfect surfaces. This rationale has underpinned the easing of lockdown restrictions in India, with public places like airports, cinema halls and malls inviting customers back with the promise of rigorous disinfection drives.
The belief that you can contract Covid-19 from touching a surface that hosts infectious germs or microbes has spawned an entire ecosystem of businesses — different companies now offer disinfectants that aim to rid not just surfaces like door handles and bus seats, but also fruits and vegetables, of infection risk.
However, a year into the pandemic, overwhelming scientific evidence points to the fact that Covid-19 is much likelier to spread through airborne transmission than by surface contact.
This means that there is a much stronger chance that you will get Covid-19 while talking to a patient — even at an appropriate distance — in a poorly ventilated room, than touching the same elevator button as one.
But, hold up. Scientists are not asking you to throw away your sanitisers just yet — what harm can clean hands cause anyone, anyway? What they are saying is that health agencies need to acknowledge that the primary risk of Covid transmission is through aerosols, and ensure the public knows as much.
What we knew, what we speculated
A year into the pandemic, the general public is now widely aware of the general safety rules: To mask, distance physically, and wash hands regularly. But with the virus still raging, experts have been flagging the lack of awareness about the transmission of the virus, and thus ineffective safety measures.
The main debate is whether the primary mode of transmission is through droplets, aerosols, or from surfaces.
Surface or fomite transmission occurs when a viable virus (able to infect) present on a surface is touched, and one’s hands then touched to the face. Precautionary measures to prevent this are disinfecting surfaces and washing hands.
Early in the pandemic, a number of studies claimed to reveal startling results for how long the SARS-CoV-2 virus survived on various surfaces.
A paper published by the Journal of Hospital Research in January 2020 suggested it could survive on metal and plastics for nine days, based on existing lab studies of other coronaviruses that caused Severe Acute Respiratory Syndrome (SARS) and Middle East Respiratory Syndrome (MERS). In March, a study in the New England Journal of Medicine suggested that the virus can survive on plastic surfaces for over three days, and on cardboard for upto 8 hours.
Such findings garnered quick attention, leading to persistent messaging around disinfection and sanitisation.
As the pandemic spread, however, aerosol experts started to sound the alarm on airborne transmission dynamics, requesting the authorities to stress on the spread of the novel coronavirus through aerosols and not just droplets or contact with infected surfaces.
Airborne, aerosol, and droplets
While ‘airborne’ and ‘aerosol’ are often used interchangeably, they actually mean different — if overlapping — kinds of transmission. Airborne transmission occurs when suspended particles of varying sizes — including cough droplets — are dispersed by air. Heavier droplets fall closer to the person who expels them, increasing risk of infection at close contact. When these droplets fall on surfaces, they become fomites.
Humans produce respiratory droplets that range from 0.1 micrometre to 1,000 micrometres in size. Larger droplets are thought to be anywhere between 5 and 1,000 micrometres in size, while what is generally known as aerosols are less than 5 micrometres. The SARS-CoV-2 virus is approximately 0.1 micrometre in size.
Aerosol transmission of a virus typically involves the virus either floating free in the air, or latching on to other aerosols — dust or pollutants, but mainly phlegm or water, which can encase the virus particles before evaporating away — and floating to larger distances.
In June 2020, a study published in the peer-reviewed Environmental Protection reported that people in polluted areas are more severely affected by Covid-19.
Aerosol transmission was previously observed in other coronaviruses too. The 2004 Amoy Gardens SARS outbreak in Hong Kong, involving nearly 300 people, was traced to the aerosolisation of faeces of one patient in drainage pipes.
Aerosols can be exhaled when simply breathing, when coughing or sneezing, and also when speaking and singing. Expulsive events like coughing or singing reportedly increase the distances they travel, as do louder voices.
In May, the US Centers for Disease Control (CDC) reconstructed a superspreader event at a choir practice in Washington. Around 61 people met for 2.5 hours on 10 March, to sing and eat. The group included one symptomatic Covid patient. By 17 March, 53 of the attendees were ill, three had to be hospitalised, and two had died.
There have been other singing events, as well as other clusters of superspreading events that have been linked to transmission indoors and in enclosed spaces like prisons and hospitals, attributed primarily to aerosol spread, driven by air currents.
Perhaps the best known “viral” exposure event was described in a study by Chinese researchers last April that retraced multiple infections from one evening at an air-conditioned restaurant in Guangzhou, China.
A five-member family, including an asymptomatic patient, ate there on 24 January 2020. Within two weeks, nine others who had dined there the same day fell sick. Four were relatives of the index patient but five others had caught the virus while seated on two different tables with others who did not get infected.
The study researchers noted that the infected individuals had been seated in the path of the airflow from the air-conditioning unit near the index patient.
“Virus transmission in this outbreak cannot be explained by droplet transmission alone,” concluded the peer-reviewed study.
Then there is also the concern of the virus lingering in the air with or after an infected person.
In a study led by Dr John Lednicky, a research professor at the University of Florida, the air around hospitalised Covid patients was sampled at distances of up to nearly 5 metres, and the team was able to obtain viable virus particles.
He explained that one of the reasons researchers are still scrambling to get data on aerosol transmission is that our technology isn’t where we need it. Capturing viable virus from air is difficult as the process of sampling itself could leave the virus unviable or effectively dead.
“Inhalation of non-viable SARS-CoV-2 will not cause Covid-19,” he added. “So, when people perform air samplings and the virus they collect is non-viable, the assumption is they pose no risk.”
More recently, a study (published on the preprint server bioRxiv) on ferrets separated by levels but connected by a PVC pipe with 90 degree turns, showed that aerosols lingered in the air and transmitted over distances greater than 1m.
Peer-reviewed findings from a study by researchers at Cambridge University, published in the Proceedings of the Royal Society A this week, show that the virus spreads more than two metres (among the social-distancing yardsticks advised) in mere seconds in poorly ventilated spaces, and that prolonged talking spreads more virus than coughing.
Said Lednicky, “When you get into particles of very small mass, it turns out they don’t fall out of the air according to the rules of gravity we are accustomed to. Instead, when humidity is relatively low, they can stay adrift for long periods of time due to upward forces (air currents) we normally don’t think about.”
Studies on fomite transmission
Conversely, studies on fomite transmission have yielded limited data.
“There are two or three possible cases in the literature that are consistent with fomite transmission, but even these cannot exclude airborne transmission,” said Dr Emanuel Goldman, professor of microbiology at Rutgers University, US, who pointed out last July in a piece for The Lancet that fears of fomite transmission might be exaggerated.
The most compelling piece of evidence, he said, was a likely transmission in China where a live virus was found on the packaging of imported, frozen seafood. Two dockworkers tested positive after handling the shipment, but it could not be confirmed that they contracted the virus because of contact with the packaging.
“On the other hand, there is evidence for lack of fomite transmission. For example, in a mixed-use building in South Korea, workers in a call centre became ill with Covid-19, infecting everyone in that office. But in the rest of the occupants of that building (almost 1,000 people), only three became positive for Covid-19 (which could have been through aerosols),” he added.
“Had there been significant fomite transmission, many more people in the building would have tested positive,” he said, referring to factors such as shared elevators.
In the July piece, he argued that “transmission by fomites (inanimate surfaces or objects) has been assumed on the basis of studies that have little resemblance to real-life scenarios”. The essence of his argument was that the studies used much larger concentrations of virus than are likely to be deposited on the surface in real-life conditions.
Experts in aerosol dispersal and atmospheric chemistry who sounded the earliest warnings stated that the early WHO recommendations of distancing by 6 feet are based on research carried out on droplets almost 90 years ago, when the technology to study sub-micron aerosols did not exist.
Recent findings show smaller aerosol particles lingering in indoor air for over 12 hours.
“The concept that the virus is transmitted through contact with the environment is primarily based on studies of mouse hepatitis virus (the best-studied coronavirus),” said Lednicky.
“Mice really don’t sneeze much. Instead, the virus is spread through contact with faeces, urine, and contaminated surfaces. But people are not mice. We don’t move about with our noses to the ground, and normally would not eat food items on the ground.”
Indeed, while the research community continues to consider fomites as a theoretical mode of transmission, multiple studies published over the past several months — including this peer-reviewed research published in the Military Medicine journal in December — seem to support the theory that real-world transmission through fomites is minimal when compared to aerosol or droplet spread.
“The most important thing is to tell people that the virus is transmitted by breathing other people’s exhaled air,” explained Dr Jose-Luis Jiminez, professor at Analytical, Environmental, and Atmospheric Chemistry Division in University of Colorado-Boulder, US.
“People have to imagine that others are exhaling invisible smoke that behaves in the air just like cigarette smoke, and they need to do whatever they can to breathe less of it. Once people understand that, they figure out what they have to do in their particular situation,” Jiminez added.
What health agencies say
Premier health agencies around the world have been slow to shift focus to aerosol transmission, with most still stressing on washing hands or disinfecting surfaces with the same emphasis as masking and distancing.
During the early days of the pandemic, the World Health Organization (WHO) continued to insist that Covid was not airborne.
FACT: #COVID19 is NOT airborne.
The #coronavirus is mainly transmitted through droplets generated when an infected person coughs, sneezes or speaks.
To protect yourself:
-keep 1m distance from others
-disinfect surfaces frequently
-wash/rub your 👐
-avoid touching your 👀👃👄 pic.twitter.com/fpkcpHAJx7
— World Health Organization (WHO) (@WHO) March 28, 2020
In July, it said, “further studies are needed to determine whether it is possible to detect viable SARS-CoV-2 in air samples from settings where no procedures that generate aerosols are performed and what role aerosols might play in transmission”.
It refers to “consistent evidence as to SARS-CoV-2 contamination of surfaces and the survival of the virus on certain surfaces”, but adds that there “are no specific reports which have directly demonstrated fomite transmission”.
The US CDC continues to stress the methods, duration, and importance of washing hands, but also warns the public to avoid poorly ventilated spaces. Last May, it said, “it may be possible that a person can get Covid-19 by touching a surface or object that has the virus on it and then touching their own mouth, nose, or possibly their eyes, but this isn’t thought to be the main way the virus spreads”.
— #IndiaFightsCorona (@COVIDNewsByMIB) December 29, 2020
“[It is] very difficult to change the perception that was initially promoted when the pandemic first started,” said Goldman. “Incorrect information was put out there by experts who had not critically assessed the scientific basis for advising deep cleaning. There were papers showing that the virus survived on surfaces for a few days. Unfortunately, the experts failed to recognise that these results were under artificial lab conditions and not in real-life scenarios.”
One of the easiest ways to make an indoor setting safer is by opening windows and encouraging cross ventilation. Air filters and purifiers are also an advantage indoors.
“Very few national health agencies stress ventilation. Most ignore this risk completely,” said Dr Lidia Morawska, aerosol science researcher at Queensland University of Technology, Australia, and member of the WHO taskforce that studied aerosol transmission of SARS in 2003. “[The authorities] should be stressing the need for good ventilation in all indoor shared spaces. Ventilation should be set on ‘high’, and air reticulation should be avoided.”
“If ventilation is inadequate to remove the virus from the air, despite social distancing and other recommendations followed, infections will occur,” she said, adding that inadequate ventilation can be helped with air purifiers.
Jiminez also stressed the importance of effective communication. “Agencies such as WHO and CDC put out guidelines and videos and tweets saying that ventilation is very important. But they never explain why,” he said. “At the same time [they] say that airborne transmission is not important. So, people are very confused, and many do not ventilate or do not understand how to do it.”
Scientist initiatives and responses
While the WHO has released guidelines discussing ventilation in the context of Covid-19, many scientists believe the UN agency hasn’t effectively emphasised its role in the spread of infection.
Several scientists and atmospheric particle experts, including Jiminez, have consequently created their own FAQ documentation on Covid transmission backed by data
Citizen scientists also created the ‘Covid is Airborne’ collective to spread awareness and petition the WHO to urgently recognise the role of aerosols.
To the contrary, places like Taiwan and Hong Kong, which have learned painful lessons from the SARS outbreak of 2003-2004, took precautions to prevent transmission by aerosols. Now, some countries have even put forth a full pandemic ventilation guides.
“The risk of inhalation exposure to the virus reduces the farther away one is from the virus emitter, but in enclosed spaces with low humidity, the virus can stay airborne and be carried by air currents long distances away from the source,” said Lednicky. “Many health agencies have failed to properly assess the danger posed by airborne SARS-CoV-2.”
“It is less contagious than measles but more contagious than tuberculosis, both of which are also airborne,” Jiminez added. “[Agencies] seem to fear that acknowledging it would cause fear and panic. But what really causes fear and panic is a pandemic that is out of control in many places, precisely because they are not telling people how the virus is transmitted, so that people can’t protect themselves.”
Handwashing and disinfecting
While scientists urge the importance of acknowledging the role of ventilation, they don’t make light of the importance of hand-washing, saying it’s an advisable hygiene practice in general.
Hand hygiene has been extremely beneficial to keeping other communicable diseases in check in the past and continues to do so today. While there is no evidence it curbs Covid-19 transmission, low occurrence of other diseases prevents healthcare systems from being more overwhelmed during crisis-time.
Goldman said there remains a theoretical possibility that if a person touches a freshly contaminated surface, and then touches their face without having washed their hands, that person could become infected.
“Washing hands breaks this potential chain of transmission,” he said. “It’s also generally good hygiene to wash hands regularly, even without the pandemic, to protect against many types of infections.”
Morawska also said she doesn’t think agency guidelines around washing hands need to be revised yet, as it could help curb transmission.
But disinfecting surfaces is just “hygiene theatre”, say experts.
“Disinfecting surfaces is most likely a waste of time and money. We should stop doing that (except perhaps in hospitals) and devote that time, money, and energy to avoiding breathing other people’s exhaled air,” said Jiminez.
Priya Kathpal, a Mumbai-based nutritionist, added that consumers should stay away from products that promise to disinfect fruits and vegetables.
“In my opinion, you don’t need disinfectants for fruits and vegetables at all,” she said. “Thoroughly washing fruits and vegetables with clean, lukewarm water is good enough to get rid of pesticides and germs.”
“In the beginning there was very little data. But now, data tells you that the fomite transmission is almost nil,” she added.
She also said regular food hygiene should be continued but there is no extra cleaning that needs to be done for the virus. It is also well established that heat and cooking renders the virus unviable rapidly, and it can’t spread through hot food.
This report has been updated with additional information