The spread of coronavirus variants in the United States has prompted some public health experts to recommend doubling up face coverings or donning medical-grade masks.

Officials initially discouraged most people from buying medical masks such as N95s and KN95s, to try to protect the supply for health-care workers. Doctors and nurses have used individual medical-grade masks for far longer than recommended as shortages have continued during the pandemic.

Although federal officials have not changed their guidance on medical masks, experts’ suggestions are prompting questions about whether and how to access these face coverings as the variants threaten the country’s progress against the virus.