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Coronavirus aerosol transmission might be even worse than we think

  • Coronavirus aerosol spread is a real risk, the World Health Organization said a few weeks ago after more than 200 researchers urged the WHO to acknowledge the issue. But the organization maintains that droplet transmission is the primary way COVID-19 spreads.
  • A new study looked at how COVID-19 moved inside the closed environment of the Diamond Princess cruise ship that was quarantined in Japan in early February, finding that aerosol transmission may be a worse phenomenon than we thought.
  • The research follows other studies that proved virus from aerosols can infect cells, and that showed taller people are twice more likely to be infected.

The Diamond Princess cruise ship gained worldwide notoriety in early February when Japanese authorities quarantined the boat in Port of Yokohama looking to contain the COVID-19 infection aboard the vessel. Eventually, 712 of the 3,711 passengers and crew on board tested positive, and 14 died by the time the Diamond Princess docked. The ship has been the subject of some studies, considering that it offered researchers a unique view of the behavior of the virus inside a population that was confined to the ship for several weeks.

The newest research might prove that one of the worst things about the novel coronavirus should be a real worry for authorities looking to contain COVID-19 outbreaks. That’s the aerosol transmission, a topic that keeps popping up in COVID-19 more and more often. The World Health Organization (WHO) acknowledged the risk of COVID-19 spread via the air a few weeks ago but still maintained that the larger saliva droplets that are ejected during talking, sneezing, and coughing are the primary way the virus spreads. The new Diamond Princess study says it can quantify the aerosol transmission inside the cruise ship.

Researchers have recently proven that the virus that can float in aerosols can replicate once it reaches cells. This was an indication that the virus can survive in the air in those microdroplets that become aerosols after the water evaporates, and float longer than the larger saliva droplets that can land on surfaces and people. A different study proposed another unexpected conclusion. People who are 6 feet tall are twice more likely to be infected with the novel coronavirus, and airborne spread is the only type of transmission that can support the finding.

Researchers from Harvard and the Illinois Institute of Technology teamed up for a study that attempted to model the transmission models of COVID-19 aboard the ship and concluded that aerosol transmission played a significant role in the Diamond Princess coronavirus epidemic. The study hasn’t been peer-reviewed, but it’s been published online in medRxiv, via The New York Times.

The researchers ran more than 20,000 simulations that took into account various particularities of the Diamond Princess COVID-19 outbreak, including patterns of social interactions, the amount of time the virus can live on surfaces, the size of particles ejected from a person’s mouth and their behavior in the air.

Over 130 simulations delivered results similar to what happened in real life aboard the ship. The researchers looked at the most “realistic” scenarios to calculate the importance of the various ways of viral transmission. They concluded that the smaller droplets were predominantly responsible for the spread of the virus on the cruise ship, accounting for 60% of new infections both at close range and at greater distances. Fomite transmission, or getting the virus from touching the same surfaces, played a smaller role.

“Many people have argued that airborne transmission is happening, but no one had numbers for it,” Harvard’s T.H. Chan School of Public Health Dr. Parham Azimi said. “What is the contribution from these small droplets — is it 5 percent, or 90 percent? In this paper, we provide the first real estimates for what that number could be, at least in the case of this cruise ship.”

So far, researchers proved that aerosol transmission is a real thing for infectious disease, including COVID-19, that aerosol viral loads are contagious, and that the aerosol spread may have been the main driver of the Diamond Princess outbreak. More research is required, and the studies should receive proper reviews from other experts.

Separate research showed that face masks could reduce droplets and aerosol transmission, whether it’s surgical masks or multi-layered homemade cloth covers. It’s unclear what quantity of virus would be enough to infect a person. But aerosols could help the pathogen reach the lower airways faster than droplets. It’s in the lungs where the virus can multiply at devastating speed and cause several life-threatening complications.

The researchers think that the Diamond Princess transmission study could help officials shape new measures that could be applied to indoor conditions, like school. The simplest is “really enforcing mask policies,” according to Illinois Institute of Technology in Chicago professor Brent Stephens. Proper masks should also be used to reduce the spread via aerosols.

Changes to ventilation may also be required to improve the safety of indoor spaces. The Diamond Princess did not recirculate air and was well ventilated, but that didn’t stop the virus from spreading.

Not all scientists agree that aerosol transmission can be the primary driver of COVID-19 spread, and The Times’ coverage is worth a read for more opinions on the matter. But even if the aerosol spread is just a minimal risk, health officials should consider measures to reduce this avenue of transmission.

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