How CDC Determines the Level of a Country’s COVID-19 Travel Health Notice

CDC uses Travel Health Notices (THNs) to alert travelers and other audiences to health threats around the world and advise on how to protect themselves.

On November 21, 2020, CDC adapted its 3-level notice system to a 4-level system for COVID-19 and updated criteria used to determine THN levels. The system was updated to align with the same incidence rate or case count thresholds adopted by recognized public health organizations and shares a common 4-level structure with the U.S. Department of State's Travel Advisoryexternal icon system.

COVID-19 Travel Recommendations can be found in two places:

The 4-level system categorizes international destinations into the following levels:

• Level 4: Very high level of COVID-19
  • Avoid travel to this destination.
• Level 3: High level of COVID-19
  • Make sure you are fully vaccinated before travel.
  • Unvaccinated travelers should avoid nonessential travel to this destination.
• Level 2: Moderate level of COVID-19
  • Make sure you are fully vaccinated before travel.
  • Unvaccinated travelers who are at increased risk for severe illness from COVID-19 should avoid nonessential travel to this destination. If you must travel and have concerns, talk to your doctor.
• Level 1: Low level of COVID-19
  • Make sure you are fully vaccinated before traveling to this destination.

CDC uses COVID-19 data reported by the World Health Organization and other official sources to make determinations about THN levels. If a destination does not provide data, their THN level is designated as "unknown" and travelers are advised to follow THN Level 4 recommendations.

Travel Health Notice Thresholds

CDC reviews case data reported to the World Health Organizationexternal icon to determine a destination's COVID-19 THN level.

THN thresholds are based on the number of COVID-19 cases in a destination.

Primary criteria for destinations with populations over 100,000

1. Incidence rate (cumulative new cases over the past 28 days per 100,000 population)
2. New case trajectory (have daily new cases increased, decreased, or remained stable over the past 28 days?)

Primary criteria for destinations with a population of 100,000 or fewer

1. COVID-19 case counts* (cumulative new cases over past 28 days)
2. New case trajectory (have daily new cases increased, decreased, or remained stable over the past 28 days?)

*CDC does not count identified imported cases (i.e., cases in travelers who were exposed in another country) against a destination's total.

Secondary criteria for determining Travel Health Notice Levels

Reported case counts and incidence rates depend on testing capacity. CDC assesses testing capacity using two secondary criteria metrics: population testing rate and test-to-case ratio. The population testing rate is the number of tests conducted per 100,000 people over 28 days. The test-to-case ratio is the number of tests conducted for each case reported during the same 28-day period. Testing data are obtained from multiple sources, including Our World in Dataexternal icon , Foundation for Innovative Diagnosticsexternal icon , and country ministries of health.

Travel Health Notice levels 1 through 4 for destinations with a population more than 100,000 people. Levels are based on combined 1) incidence rate (primary criteria) and 2) testing data (secondary criteria) *

*Incidence rate is the primary criteria for destinations with a population more than 100,000 people. Testing data are the secondary criteria and that data includes both the testing rate (column 1) and test-to-case ratio (column 2). The resulting health notice levels are shown in rows 3-11 of columns 3-6.

Travel Health Notice levels 1 through 4 for destinations with a population of 100,000 people or fewer. Levels are based on combined 1) case count (primary criteria) and 2) testing data (secondary criteria) *

*Case count is the primary criteria for destinations with a population fewer than or equal to 100,000 people. Testing data are the secondary criteria and that data includes both the testing rate (column 1) and test-to-case ratio (column 2). The resulting THN levels are shown in rows 3-11 of columns 3-6.

Population testing rates of more than 1,500 tests per 100,000 people over 28 days are considered sufficient to provide an accurate representation of COVID-19 in the destination. Rates less than or equal to 1,500 tests per 100,000 people over 28 days may signify concerns that testing is insufficient and may not provide an accurate representation of the incidence rate in the destination. The cutoffs for evaluating population testing ratesexternal icon have been adapted from the WHO guidelines.

The WHO determined a test-to-case ratio greater than or equal to 10 as the minimum indicator of sufficient surveillance capacity. A test-to-case ratio of less than 10 tests per case might indicate restrictive testing, or that only symptomatic people are being tested and undercounting the incidence rate (primary criteria). The preferred level is a test-to-case ratio of more than 30. The cutoffs for evaluating test-to-case ratios pdf icon [PDF - 18 pages]external icon have been adapted from the WHO guidelines.

When both the population testing rates and test-to-case ratios are high, CDC has confidence in a destination's reported incidence. If either the population testing rate or test-to-case ratio is low, CDC has less confidence that the reported incidence accurately depicts the COVID-19 situation in the destination. In this situation, CDC adjusts a destination's THN level as shown in the tables above.

Raising a Travel Health Notice

CDC raises a destination's THN level when the incidence rate (or case count) and testing metrics meet the THN threshold for a higher level and remain at that level for 14 consecutive days. The THN level may be raised before 14 days if there is a large increase in COVID-19 cases reported.

Lowering a Travel Health Notice

CDC lowers a destination's THN level when the incidence rate (or case count) and testing metrics meet the THN threshold for a lower level and remain at that level for 28 consecutive days. Vaccination coverage rates and vaccine performance will be considered when determining if the THN level can be lowered before 28 days.

Special Considerations

Additional information such as new variant of concern, vaccination rates, hospitalizations, and imported case counts may be considered when determining a THN level, especially when inconsistencies or other concerns are reported. CDC works with country authorities through CDC country or regional offices to gather additional data as appropriate.

Public link

Please use the above public link if you want to share this noodl on another website.