Among strategies to prevent COVID-19, CDC recommends all unvaccinated persons wear masks in public indoor settings. Based on emerging evidence on the Delta variant, CDC also recommends that fully vaccinated persons wear masks in public indoor settings in areas of substantial or high transmission.Fully vaccinated persons might consider wearing a mask in public indoor settings, regardless of transmission level, if they or someone in their household is immunocompromised or is at increased risk for severe disease, or if someone in their household is unvaccinated (including children aged <12 years who are currently ineligible for vaccination).
The principal mode by which persons are infected with SARS-CoV-2 is through exposure to respiratory fluids carrying infectious virus. The risk for SARS-CoV-2 transmission in outdoor settings is low. CDC recommends that public health practitioners and organizations prioritize prevention strategies for indoor settings.
Proven effective strategies against SARS-CoV-2 transmission, beyond vaccination, include using masks consistently and correctly, maximizing ventilation both through dilution and filtration of air, maintaining physical distance and avoiding crowds. Basic public health measures such as staying home when sick, handwashing and regular cleaning of high-touch surfaces should also be encouraged.
Given the spread of the highly transmissible Delta variant, local decision-makers should assess the following factors to inform the need for layered prevention strategies across a range of settings: level of SARS-CoV-2 community transmission, health system capacity, vaccination coverage, capacity for early detection of increases in COVID-19 cases and populations at risk for severe outcomes from COVID-19.
COVID-19 vaccination remains the most effective means to achieve control of the pandemic. In the United States, COVID-19 cases and deaths have markedly declined since their peak in early January 2021, due in part to increased vaccination coverage. However, during June 19–July 23, 2021, COVID-19 cases increased approximately 300% nationally, followed by increases in hospitalizations and deaths, driven by the highly transmissible B.1.617.2 (Delta) variant of SARS-CoV-2, the virus that causes COVID-19.
Unvaccinated persons, as well as persons with certain immunocompromising conditions remain at substantial risk for infection, severe illness and death, especially in areas where the level of SARS-CoV-2 community transmission is high.
The Delta variant is more than two times as transmissible as the original strains circulating at the start of the pandemic and is causing large, rapid increases in infections.
A person’s risk for SARS-CoV-2 infection is directly related to the risk for exposure to infectious persons, which is largely determined by the extent of SARS-CoV-2 circulation in the surrounding community.
Unvaccinated persons remain at risk for infection, severe illness, and death. Advanced age, pregnancy and an increasingly well-defined set of underlying medical conditions increase the risk for serious outcomes from COVID-19 among unvaccinated persons.
In addition, long-standing systemic health and social inequities have put members of certain racial and ethnic minority groups at increased risk for serious illness and mortality from COVID-19. Persons taking immunosuppressive medications, persons with hematologic cancers, and hemodialysis patients, among others, have shown reduced immunologic responses to COVID-19 mRNA vaccination and might remain at increased risk for severe COVID-19 following vaccination.
CDC recommends unvaccinated persons should continue following all prevention strategies, including wearing a mask, until they are fully vaccinated.
Immunocompromised persons should continue to take all recommended precautions until advised otherwise by their health care provider. Although COVID-19 vaccines authorized in the United States remain effective against severe outcomes from SARS-CoV-2 infection, a small proportion of persons who are fully vaccinated may become infected.
Emerging evidence suggests that fully vaccinated persons who do become infected with the Delta variant are at risk for transmitting it to others.