As University of Iowa students and faculty return to in-person teaching and learning after more than a year of pandemic disruptions, members of the campus community are being encouraged to follow best practices – including vaccination, mask-wearing, and social distancing where possible – to protect against the spread of COVID-19.

But with coronavirus case counts rising throughout the state, some local leaders in Iowa are advocating additional steps to slow COVID-19 transmission. Iowa City officials last week reinstated the city’s mask mandate, requiring face coverings in most public places, despite a state law banning local governments from requiring mask-wearing. While the University of Iowa strongly encourages the use of face masks, state law and Board of Regent policy prohibit the school from requiring face coverings, according to UI officials.

Still, Iowa City’s masking order, coupled with recent changes in the Centers for Disease Control and Prevention’s recommendations on mask-wearing, has prompted renewed questions about the role of face coverings. Fred Gerr, professor emeritus of occupational and environmental health, answered a couple of key questions about masks as a mitigation measure.

What is known about the effectiveness of face masks in reducing coronavirus transmission, particularly the highly infectious Delta variant?

The use of face masks is a proven method of reducing the spread of COVID-19, and numerous studies examining the effect of face mask use are available in the medical literature. A list of such papers and the conclusions reached by the authors can be found here. These studies were conducted before the Delta variant became the dominant virus causing COVID-19 in the United States. However, because the Delta variant is an airborne coronavirus just like all previous viruses that cause COVID-19, there is no basis to believe that the benefits of masks will be any different.

Although the studies demonstrating benefits of face masks to prevent the spread of COVID-19 were conducted primarily on populations using cloth or disposable paper masks, it is important to remember that the meaning of the term “face mask” may differ from person to person. At a minimum, a face mask is a cloth or disposable paper mask that covers the nose and mouth of the wearer. The purpose is to reduce the spread of airborne virus by the wearer (in their exhaled breath) should they be infected with COVID-19 virus. Such spread is possible because some infected persons feel perfectly well and may not know to self-isolate. 

Face masks are not designed to protect the wearer from inhalation of airborne virus, although they may provide some limited inhalation protection. A higher level of protection against inhalation of airborne virus can be obtained by the use of a filtering facepiece respirator (e.g., the N-95 respirator). These respirators best provide such protection if an effective seal is made against the skin of the wearer. A procedure to ensure a good fit of an N-95 respirator to a wearer’s face can often be conducted by staff members of an organization’s safety and health program. 

At this stage of the pandemic, how does mask-wearing fit into the public health response to COVID-19?

Mask use continues to be a critically important component of the public health goal of minimizing the spread of COVID-19.

It is well-known that COVID-19 is spread predominantly by airborne transmission. Before the availability of highly effective and exceptionally safe vaccines for primary prevention of COVID-19 infection, face masks, social distancing, improvements in ventilation, and related measures were the best available protection against the spread of COVID-19.

When initially offered, COVID-19 vaccination provided a high level of protection against infection with the virus.  Recently, it has become clear that the Delta variant is much more infectious than earlier COVID-19 virus variants. As a result, the number of vaccinated persons becoming infected with the Delta variant has increased (this phenomenon is sometimes called “breakthrough” infection). 

Fortunately, the vaccines still prevent serious illness, hospitalization, and death due to infection with all variants of the COVID-19 virus. Unfortunately, the vaccine is not, itself, completely effective at preventing the spread of COVID-19 infection, especially when caused by the Delta variant. This reality is the basis for renewed recommendations for use of face masks. As noted above, because a substantial proportion of persons with breakthrough infection feel perfectly well (but can still spread the virus) universal use of face masks will reduce the spread of the virus and keep our community safer and healthier. 

Additional links of interest:

• CDC’s Interim Public Health Recommendations for Fully Vaccinated People
• Annotated bibliography of studies on mask effectiveness