In further evidence for the airborne transmission of the novel coronavirus, a COVID-19 positive person possibly exposed 23 fellow passengers to the infection in a poorly ventilated bus.

An investigation into the outbreak in Eastern China looked at 128 individuals in two buses, the second of which had 68 passengers, including a COVID-19 infected person who had been in contact with people from Wuhan. In both buses, central air conditioners were in indoor recirculation mode.

The passengers had not been wearing masks as there was no public awareness of COVID-19 in the city at that time.

A Look at How the Infection Spread

The findings, published in JAMA Internal Medicine, showed that individuals in bus 2 had a 34.3% higher risk of getting COVID-19 compared with those in the other bus.

Since the infection spread to not just those sitting in immediate proximity and affected those even beyond the six-feet distance, airborne spread of the virus through smaller particles (aerosols) that stay in the air and travel farther than heavier droplets ‘may at least partially explain the markedly high attack rate observed’, the study said.

The authors note, “Passengers sitting closer to the index patient on the exposed bus did not have statistically higher risks of COVID-19 as those sitting further away. If COVID-19 transmission occurred solely through close contact or respiratory droplets during this outbreak, the risk of COVID-19 would likely be associated with distance from the index patient, and high-risk zones on the bus would have more infected cases.”

Moreover, only one passenger sitting by an openable window (green oval shaped in the graphic) developed an infection.

In a further contact investigation of the 23 patients, it was found that they had passed on the infection to at least 20 others (who would be the ‘tertiary’ cases).

“These data suggest that forced, circulating air might play an important role in airborne spread of the virus, and gatherings in enclosed settings with minimal air ventilation should be limited,” the researchers conclude.

How Do You Stay Safe?

On 8 July, the World Health Organization acknowledged that there is “emerging evidence” that the novel coronavirus may be airborne after an open letter by 239 scientists asked the agency to revise its guidelines.

A WHO official said that airborne transmission in crowded, closed or poorly ventilated spaces cannot be ruled out, but further assessment is needed for airborne transmission to be definitive.

Watch this explainer video to understand how the virus lingers in the air:

These are some ways you can stay protected from the coronavirus aerosols:

• To put it simply: Wear your mask.
• Physical distancing and handwashing are still extremely important. But they may not be enough.
• Preventing airborne transmission would mean avoiding crowded indoor spaces as much as possible.
• If you do spend time indoors, do not forget to wear a mask, except maybe around family and friends who you know have stayed safe.
• Ensure enough fresh air is circulating through a room.
• Open windows and doors as much as possible.
• If you can, upgrade the filters in your home air-conditioning systems.
• If schools, offices, malls and stores reopen, the ventilation systems may need to add powerful new filters to avoid recirculating the same air.
• In the right setting, the use of ultraviolet lights that can kill the virus may also be considered to prevent transmission through smaller droplets.
• Remember, stagnant air inside closed doors could be your enemy.