Delaware was used as a model for a report on mask use and COVID-19 transmission. Here’s what it says

On Nov. 6, the CDC released a report with the title “Declines in SARS-CoV-2 Transmission, Hospitalizations, and Mortality After Implementation of Mitigation Measures— Delaware, March–June 2020.”

Easy to miss, all things considered, but it came across the r/Delaware subreddit the other day.

In short, a team of researchers from the CDC Epidemic Intelligence Service, the CDC COVID-19 Response Team and the COVID-19 Outbreak Response Team of the Delaware Division of Public Health studied the data from Delaware from the beginning of the lockdown in March to the end on June 1. (We’re currently in Phase 2.)

Stay-at-home orders were issued on March 24, 13 days after the first COVID-19 case was reported in Delaware, and a statewide public mask mandate (which we are still under) was issued on April 28. Contact tracing started on May 12.

What did they find? To quote:

The relationship among implementation of mitigation strategies, case investigations, and contact tracing and COVID-19 incidence and associated hospitalization and mortality was examined during March–June 2020. Incidence declined by 82%, hospitalization by 88%, and mortality by 100% from late April to June 2020, as the mask mandate and contact tracing were added to case investigations and the stay-at-home order.

Those are pretty big numbers, and compelling evidence that mitigation strategies, especially multiple mitigation strategies working together, can and do cause a decline in COVID-19 cases and mortality.

There were some complications. For one, a whopping 83% of interviewed patients refused to disclose contacts or couldn’t recall contacts for tracing.

Second, cases were contacted a median of 8 days after receiving their positive test result and 5 days after report of this result to DPH. Earlier initiation of case investigation might increase recall and early identification of close contacts and thus prevent further disease transmission. Lastly, 22% of contacts could not be reached for reasons designated as “other,” an interaction outcome in case investigations and contact tracing reserved for circumstances interviewers could not address without additional information. Daily and weekly data monitoring to provide additional information for those with “other” as an interaction outcome could increase the number of persons reached.

It’s worth noting that the COVID Alert app would roll out later, in September, and the app allows users to do daily symptom check-ins and also allows users’ contacts to remain anonymous so patients don’t have to voluntarily disclose contacts to health authorities by name, something a lot of people are understandably uncomfortable doing.

The report also noted that they didn’t not have data on adherence to stay-at-home and mask usage. Anecdotally, Wilmington was and still is a place where you don’t see people in public without a mask unless they’re driving or walking outdoors alone and far from other people. According to a survey taken in September, 78% of Delawareans are pro-mask.

The results are not a shock, at least if you live in a place like Delaware that locked down in March. Cases and deaths did drop dramatically. The mask mandate kept the numbers reasonable through the summer and early fall. Now, with winter coming and cases rising again as outdoor dining and socializing move indoors again, we could be looking at Phase 1 again, where fewer nonessential businesses and day cares can stay open under strict guidelines.

We could also be looking at stay-at-home orders for the holidays — not that the CDC guidelines for even small mixed-household family holiday gatherings (which include things like opening windows to the cold air for ventilation and everyone bringing their own food and drinks) aren’t discouraging enough.