5 December 2023

Explainer: What we know about masking and Monkeypox prevention

Annie Lab looks into the science behind mask wearing and the possibility of airborne transmission of the monkeypox virus.

On June 6, the Centers for Disease Control and Prevention of the United States updated their Travel Health Advisory, recommending travelers to wear a mask to “protect themselves from many diseases, including monkeypox.”

By the time CDC issued the advisory, there had been over 1,200 reported global cases of monkeypox, 45 of which were confirmed in the U.S. The disease caused by the monkeypox virus has symptoms similar to, but less severe than, smallpox.

On the same day a tweet that has about 4,600 retweets and 18,000 likes implied the monkeypox virus has not been scientifically proven as airborne and criticized CDC’s advisory as not “following science.”

The tweet above questions CDC’s recommendation on masks when monkeypox has not been confirmed as an airborne virus.

Another tweet by John Cordillo, a TV host for an American right-wing media, made a similar claim, accusing CDC of attempting to “control” citizens without scientific evidence. This tweet got 17,700 likes and was shared 6,500 times.

On the same day in the evening, the media in the U.S. reported CDC had removed the mask recommendations from the travel health notice.

Left: CDC’s mask recommendation on their website uploaded on June 6 (screenshot from Wayback machine archive);
Right: The recommendation has since been deleted from their website on June 7 (screenshot from CDC’s Travel Notice webpage)

Annie Lab investigated the validity of the claims by exploring how much we know about the science of wearing face masks against monkeypox and why CDC retracted its advisory.

What face masks prevent

Face masks have been proven as an effective medium of protecting people from various methods of transmission, most notably by reducing the emission of virus-laden droplets by the wearer. According to the CDC, it also reduces inhalation of those droplets by the wearer.

As opposed to the assumptions in the above tweets, masks are not primarily used to block aerosol and airborne transmissions although masking does help, as indicated by research.

Analyzing the available epidemiological information about monkeypox, both CDC and The World Health Organization say it can be transmitted via respiratory droplets.

WHO also says it can be transmitted through “possibly short-range aerosols,” suggesting that it could be airborne to a certain degree.

But the role of masks in the case of monkeypox seems to be to safeguard individuals against infections by respiratory droplets.

The New York Times reported that medical experts suspect airborne transmission could play a small yet significant role in the spread of monkeypox infections, warning that denying the possibility altogether could be misleading to understanding the future implications of this disease.

However, according to the report, a consensus on this matter has not been reached yet as the situation continues to develop.

CDC’s retraction of the advisory

Annie Lab reached out to CDC and asked why the recommendation was removed so quickly.

A spokesperson said in an email on June 9 that the guidance had been reversed due to the confusion caused.

However, the agency added that it still recommends wearing N95 masks in “high-risk situations,” including for household contacts and healthcare workers, or for other people who may have been in close contact with an infected individual.

Close or direct contact — the main reason for infection

Health authorities say the primary reason for human-to-human transmission is close or direct contact with an infected individual’s lesions, body fluids or contaminated materials as well as through sexual contact.

Vijaykrishna Dhanasekaran, a virologist and associate professor at the School of Public Health at the University of Hong Kong told Annie Lab in an email that monkeypox cannot be classified as an airborne disease.

Respiratory droplets containing the virus are thought to be large and heavy. They fall to the ground quickly but transmission could still occur when people have face-to-face contact in very close proximity.

“More data is needed to understand if there is any potential for such aerosolization as the virus evolves and spreads. Something we should keep an eye on,” he said.

Another expert from the university, clinical virologist Siddharth Sridhar from the Department of Microbiology, said that while the main route of transmission is close contact with the skin wounds, or lesions, of an infected person, transmission by respiratory droplets is possible.

Additionally, he added that monkeypox is currently a growing epidemic within the men-who-have-sex-with-men (MSM) community and the primary reason for transmission is presumably intimate contact.

Health organizations around the world have adopted measures of prevention and control.

The National Health Service of the United Kingdom and the Centre for Health Protection in Hong Kong have advised the public to stay alert and take precautions.

CHP lists wearing protective gear such as surgical masks and gloves when interacting with ill people or animals as one such method of avoiding contracting the virus as well as an immediate hand wash.