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Pandemic Data Outlook

Destination Unknown for COVID-19 Data from Travelers

In the United States, non-resident data on COVID-19 cases, tests, and vaccines are not regulated in any way. The absence of governance leads to states presenting data in any format or disregarding it altogether despite the capacity of this data to have major impacts on trends and rates, especially during periods of frequent travel.

Beth Blauer, Associate Vice Provost, JHU
December 6, 2021

As we enter the holiday season and many people begin to travel to visit friends and family, we here at the Pandemic Data Initiative encourage you to do so as safely as possible. If you must travel, get tested prior to and after your trip or your participation in big holiday parties, get vaccinated, and limit exposure to those who remain unvaccinated.

Incorporating non-residents into U.S. state data pipelines has been complicated since the first COVID-19 tests were administered. Due to a lack of federal guidance on the issue, states have been able to choose whether they provide resident and non-resident data separately, combine resident and non-resident data, or ignore non-resident data altogether. Each process provides different benefits and complications, especially when the way the data are handled affects information gathered on testing, cases, and vaccinations.

Cases and Tests

Travel likely increases spread of the SARS-CoV-2 virus,1 leading many policymakers to prohibit or discourage interstate travel at various stages of the pandemic.2,3 However, it is impossible to prevent travel entirely, so data from non-residents will inevitably enter state data streams.

A particular conundrum is on-site testing in airports, as there are no established rules for reporting the data, and it could significantly impact reports from major travel hubs such as Chicago, Dallas, Los Angeles, Miami, and New York. Due to the limits on travel except when necessary and asymptomatic, the tests coming out of airports should be frequently negative. Adding a surplus of negative tests from non-resident travelers could artificially decrease a region’s positivity; however, these non-residents are still in the area and contributing to potential spread, so including their data in state totals could be appropriate.

Once again, each state handles this differently. Florida only reports data on residents,4 so tests from travelers in the Miami airport are removed from state totals. California reports on all tests administered in the state including detention centers and immigration facilities, so travelers through LAX would be accounted for in California testing data.5 However, some regions, such as San Diego,6 use total tests administered to residents and non-residents as the denominator in positivity calculations, but only count resident cases in the numerator, artificially reducing testing positivity.

COVID-19 testing exists to provide a better understanding of disease spread in a community and to assess the allocation of testing resources. Both are better served when non-resident data is applied to the region in which it was collected. If a person has SARS-CoV-2 and travels through Dallas, people in Dallas should know there was a case, whether that individual has a Texas driver’s license or not. The best way to handle non-resident testing data would then be to disaggregate data as resident and non-resident, which clearly explains the methodology behind the data and does not remove valuable information. Data should also be shared between states so that local health departments are alerted when residents returning from travel have contracted COVID-19.


The lack of vaccination record-sharing between states leads to major complications, including inflated and deflated reports of vaccination levels in different areas. Many U.S. vacation homes and destinations are in rural areas,7 which currently have some of the lowest vaccination rates in the United States.8 If many non-residents received vaccinations while working remotely or staying in their vacation homes, then the vaccination rates of those counties may be artificially inflated. he denominator for vaccination rate is the number of vaccine-eligible residents in the county, based on the U.S. Census. If non-residents were not registered in the area on the census, then they are not counted in the theoretical vaccine-eligible population total. This means that the undervaccination crisis in rural counties could be more severe than data currently shows.

Alternatively, if people are fleeing cities to live at vacation homes or to travel the country, then vaccination rates in cities could be artificially decreased. The number of vaccine-eligible people is not reduced just because many people decided to leave and travel during the pandemic. If a city’s population was 500,000 before the pandemic and 450,000 during the pandemic, calculations will all be performed based on the pre-pandemic number. And, even if people stayed in their state of residence but crossed county lines to get a vaccine where one was available, then the vaccination rate in their home county may be artificially decreased. This makes arbitrary vaccination coverage goals useless as the numbers reported today are probably inaccurate due to vaccinations performed outside of a person’s home jurisdiction.

This lack of communication between states has also given some people the ability to circumvent FDA guidelines and procure additional vaccine doses by crossing state lines and claiming they are uninsured.9 For example, people who are fully vaccinated in Maryland could drive less than an hour into Delaware and receive an additional dose by claiming that they have yet to be vaccinated. Delaware health officials have no way of knowing that these individuals have already been vaccinated in another state, so they will provide the vaccine.

The best solution for these travel issues is for states to develop interconnected data systems. States have already shown that they can share data with each other in near real time through Prescription Drug Monitoring Programs, which track prescription and issuance of certain medications. A similar system for sharing vaccination status and disease information should be implemented.

Regardless of where your travels take you this holiday season, we encourage you to do so safely. And we hope that soon the states can determine what to do with your data when you travel.


  1. M. Chang, R. Kahn, Y. Li, C. Lee, C.O. Buckee, H. Chang, Modeling the impact of human mobility and travel restrictions on the potential spread of SARS-CoV-2 in Taiwan medRxiv. (2020)
  2. D. Wlodkowski, Governor Tells Out-of-Staters Not to Travel to Maine ‘For an Early Vacation', 24 March 2020.
  3. F. Brown and M. Marples, Covid-19 travel restrictions and safety guidance state by state, CNN, 04 October 2021. (Accessed 30 November 2021).
  4. COVID-19 Weekly Situation Report: State Overview, Florida Department of Health, 30 November 2021. (Accessed 03 December 2021).
  5. Tracking COVID-19 in California, Testing for COVID-19, 02 December 2021. (Accessed 03 December 2021).
  6. County of San Diego COVID-19 Weekly Update, 24 November 2021. (Accessed 30 November 2021).
  7. E. Glusac, Sizing Up the Rural-Urban Travel Divide: Who’s Up and Who’s Down, The New York Times, 06 October 2020. (Accessed 30 November 2021)
  8. E. Dong, L. Gardner, The relationship between vaccination rates and COVID-19 cases and deaths in the USA, 21 September 2021. (Accessed 13 October 2021).
  9. B. Teitell, Lying about vaccination status. Crossing state lines. Pretending to forget ID. Some people are going to intense lengths to get unauthorized COVID booster shots, The Boston Globe, 06 August 2021. (Accessed 30 November 2021).

Title image by xlibber on Wikimedia Commons licensed by Creative Commons Attribution 2.0 Generic (CC BY 2.0).

Beth Blauer, Associate Vice Provost, JHU

Beth Blauer is the Associate Vice Provost for Public Sector Innovation and Executive Director of the Centers for Civic Impact at Johns Hopkins. Blauer and her team transform raw COVID-19 data into clear and compelling visualizations that help policymakers and the public understand the pandemic and make evidence-based decisions about health and safety.