Mask Mandates and Infection Trends

A Message from the COVID-19 Coordinator


  • More on masks, mandates, and public transportation
  • Updates on campus infection trends and a new reporting format

Dear Members of the Yale Community,

This week much of the national conversation about COVID-19 has focused on masking. As a result of a court order issued by a federal judge in Florida on April 18, the Centers for Disease Control and Prevention (CDC) removed its mandate requiring masks on public transportation vehicles and at transportation hubs.

This week, I will provide additional information about the CDC’s action. I will also provide updated information about COVID-19 infections on Yale’s campus and preview a new format for presenting this data on the Yale COVID-19 website.

Should I still wear my mask when using public transportation?

The decision by the federal judge in Florida was not based on public health considerations but focused primarily on the CDC’s authority to issue mandates. The CDC, although removing its mandate in response to the court order, strongly recommends that people continue to wear masks in indoor public transportation settings at this time.

Masks are most protective when everyone is wearing them because they trap infectious particles and prevent them from circulating. However, as I have written previously, high-quality masks, such as those made available through Yale, also provide a benefit for the wearer—by filtering out circulating infectious particles—even if other people around them are not wearing masks. So, wearing a mask in public transportation settings is a good idea, especially when crowds are large and when the adequacy of ventilation is uncertain or if you are at high risk for severe disease from COVID-19.

The recent court decision and subsequent CDC actions do not affect Yale’s policies. More specifically, our university mask guidance remains unchanged, and masking is still required on campus transit vehicles, such as shuttle buses.

What are the infection trends on campus, and what’s driving them?

Looking at the pattern of positive COVID-19 test results on campus can reveal certain trends and offer insight into ways that infections might be prevented. In order to demonstrate these patterns and in response to requests from the community for additional information, we plan to change the format for reporting positive COVID-19 tests on our public website. Below is a preview of this new format.

(Click on the image above for a larger view of the graph.)

This new format not only provides a different graphical representation of the test data, but also now includes information about positive results from tests performed outside of the Yale testing program and self-reported to the university. Therefore, the numbers of positive tests in the new format may vary from those presented previously on the public site.

The graph above shows that positive tests among students on our campus have recently come in waves. More specifically, the highest numbers of positive tests typically occur after the weekends.

Additional information from Yale’s Contact Tracing Team (YCCT) indicates that many of these positive tests, at least among students, are associated with exposures during unmasked interactions with others — at gatherings, indoor dining or bars, or time spent in close contact with someone who later tested positive. A summary of the YCCT findings can be seen below.

(Click on the image above for a larger view of the graph.)

This graph emphasizes once more the efficacy of masks in helping to prevent transmission. More information about masking can be found on Yale’s Mask Requirements and Guidance web page.

Of course, anyone who chooses to wear a mask in any situation should feel comfortable doing so. It is important that we respect and support those choices and that we continue to care for ourselves and each other as we navigate ever-changing public health conditions and guidance.

Stephanie S. Spangler, M.D.
Vice Provost for Health Affairs and Academic Integrity
Clinical Professor of Obstetrics, Gynecology and Reproductive Sciences
University COVID-19 Coordinator