There has been a significant question about the degree to which Thanksgiving holiday and associated travel and social gatherings may have contributed to transmission of #COVID19. Here I try to briefly address this question. 1/8

Based on known incubation periods ( https://www.nejm.org/doi/full/10.1056/NEJMOa2001316), we expect, on one end, some infections arising on Nov 26 to become symptomatic on Nov 30 and on the other end, for some infections arising on Nov 30 to become symptomatic on Dec 6. 2/8

This brackets the window where we expect most of the increased case load to be. However, most states only list cases based on date of report rather than date the case became symptomatic. This causes jitter that's hard to deal with when looking for a Thanksgiving effect. 3/8

I focus on states reporting cases based on symptom onset (or specimen collection when symptom onset is not available), were I found Ohio ( https://coronavirus.ohio.gov/wps/portal/gov/covid-19/dashboards/overview), Georgia ( https://dph.georgia.gov/covid-19-daily-status-report) and Massachusetts ( https://www.mass.gov/info-details/covid-19-response-reporting) with data available for download. 4/8

If we plot cases by symptom onset / specimen collection date and highlight the expected window of Nov 30 to Dec 6 we get the following, where there appears to be a bump in cases in this expected window of time. 5/8

This can perhaps be seen more clearly by plotting weekly total cases leading up to the 7-day period of Nov 30 to Dec 6. Here, it's very clear that there is bump in case counts in the week following Thanksgiving (marked by dashed line). 6/8

This ranges from an 11% bump for Ohio, a 23% bump for Georgia and a 41% bump for Massachusetts, based on comparison to a linear extrapolation from the 2 previous weeks. 7/8

The week with symptom onset between Dec 7 to Dec 13 has not completely filled in yet, and so the apparent drop after Thanksgiving week may become less sharp as data continues to fill in. 8/8