Guidance for Implementing COVID-19 Prevention Strategies in the Context of Varying Community Transmission Levels and Vaccination Coverage

Athalia Christie, MIA; John T. Brooks, MD; Lauri A. Hicks, DO; Erin K. Sauber-Schatz, PhD; Jonathan S. Yoder, MSW, MPH; Margaret A. Honein, PhD


Morbidity and Mortality Weekly Report. 2021;70(30):1044-1047. 

In This Article

Abstract and Introduction


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.[1] 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. Available data indicate that the vaccines authorized in the United States (Pfizer-BioNTech, Moderna, and Janssen [Johnson & Johnson]) offer high levels of protection against severe illness and death from infection with the Delta variant and other currently circulating variants of the virus.[2] Despite widespread availability, vaccine uptake has slowed nationally with wide variation in coverage by state (range = 33.9%–67.2%) and by county (range = 8.8%–89.0%). Unvaccinated persons, as well as persons with certain immunocompromising conditions,[3] 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, which could compromise the capacity of some local and regional health care systems to provide medical care for the communities they serve. Until vaccination coverage is high and community transmission is low, public health practitioners, as well as schools, businesses, and institutions (organizations) need to regularly assess the need for prevention strategies to avoid stressing health care capacity and imperiling adequate care for both COVID-19 and other non–COVID-19 conditions. CDC recommends five critical factors be considered to inform local decision-making: 1) level of SARS-CoV-2 community transmission; 2) health system capacity; 3) COVID-19 vaccination coverage; 4) capacity for early detection of increases in COVID-19 cases; and 5) populations at increased risk for severe outcomes from COVID-19. 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,[2] 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.[4,5] CDC recommends that public health practitioners and organizations prioritize prevention strategies for indoor settings. No one strategy is sufficient to prevent transmission, and multiple interventions should be used concurrently to reduce the spread of disease.[6] Proven effective strategies against SARS-CoV-2 transmission, beyond vaccination, include using masks consistently and correctly,[7,8] maximizing ventilation both through dilution[9,10] and filtration[11] of air, and maintaining physical distance and avoiding crowds.[12,13] Basic public health measures such as staying home when sick, handwashing, and regular cleaning of high-touch surfaces should also be encouraged.

*Point-in-time information is available from CDC COVID Data Tracker.
Persons are considered fully vaccinated if ≥2 weeks have elapsed following receipt of the second dose in a 2-dose series of Moderna or Pfizer-BioNTech mRNA COVID-19 vaccine, or ≥2 weeks following receipt of 1-dose of Janssen (Johnson & Johnson) vaccine. Data are available from CDC COVID Data Tracker.