Less than a week after all D.C.-area jurisdictions reached the Centers for Disease Control and Prevention’s measure for “substantial” COVID-19 transmission, D.C. and Prince George’s County in Maryland now report “high” transmission of the virus.

The CDC measures transmission levels based on two metrics: the positivity rate and the number of new infections out of 100,000 residents, both taken over seven days. “Substantial” transmission is considered to be 50-100 new cases per 100,000 residents over the past week, or a positivity rate between 8% and 10%. “High” transmission is 100 or more cases per 100,000, and a positivity rate at 10% or higher.

As of Wednesday, D.C. reported 123 new cases per 100,000 residents in the past seven days, and a positivity rate of 3.9%. Prince George’s County reported 110 new positive cases per 100,000 residents in the past seven days, and a positivity rate of 5.8%.

In D.C., deaths from the virus have not trended upward with cases, but hospitalizations due to COVID-19 have increased by 64.82% over the past seven days, according to CDC data. Still, the number of patients hospitalized with the virus in D.C. remains far lower than during previous case surges in the pandemic. During the spring 2020 peak, more than 450 people were hospitalized with the virus. As of Aug. 9, the city reported that 56 people were currently hospitalized due to COVID-19.

D.C.’s coronavirus tracking dashboard, which uses metrics for measurement separate from the CDC, shows that the average rate of daily cases per 100,000 residents has tipped into the “substantial” community spread zone as of Aug. 8. Since April, community spread levels stayed in either the moderate or minimal zones, dipping as low as 1.3 in June. Now, the city is reporting a rate of 18.1 average new cases per 100,00 residents — the highest that number has been since late March 2021. According to the Washington Post’s regional coronavirus tracker, the city is averaging a total of 132 new cases a day; in late June and early July, that number dropped into the singe digits.

During a press conference announcing a vaccine mandate for government workers on Tuesday, D.C. Health Director LaQuandra Nesbitt said that younger, unvaccinated residents are driving the uptick in cases, especially as the highly transmissible Delta variant takes hold as the dominant virus strain in the U.S.

“What’s driving our increase in cases right now is really that 25-34 year old population,” Nesbitt said. “It’s also important to note that … the majority of our cases since the vaccines became available are occurring in people who are not vaccinated.” 

The CDC reports that roughly 53% of D.C.’s population is fully vaccinated. While Nesbitt said city officials have not seen obvious racial disparities emerge in infections for the 25-34 age group, Black residents are vaccinated at half the rate of their white counterparts. Throughout the vaccination rollout, vaccination rates for residents in predominantly Black wards have lagged behind wealthier, whiter wards.

In Prince George’s County, the county’s health department reported 972 new cases in the first week of August – a seven-fold increase from the case count reported in the first week of July. While the county is not reporting an increase in deaths (the number of Prince George’s residents dying from the virus each week remains at the lowest it’s ever been during the pandemic), hospitalizations have increased by 73% in the past week. An average of 52 people are hospitalized weekly with the virus, according the county – up from an average of 12 in early July. Still, this remains well below the surges experienced in spring 2020 and January 2021, when average weekly hospitalizations surpassed 200.

According to CDC data, roughly 54% of the county’s population has been fully vaccinated.

Prince George’s County has not published vaccine “breakthrough” data, but in D.C., vaccinated individuals make up about 3% of all infections reporting from January through Aug 3, according to the city. During the press conference on Tuesday, Nesbitt said that the city is seeing an increase in the number of vaccinated individuals testing positive for the virus, as well as an uptick in vaccinated people being hospitalized. Since vaccines became available in January, Nesbitt said, fully vaccinated residents have made up about 1-2% of hospitalized cases — but now, around 10% of hospitalized cases are in vaccinated people, she said. DC Health declined to confirm those numbers with DCist on Wednesday, but said the dashboard with breakthrough data — including hospitalizations — would be updated Thursday afternoon.

Still, Nesbitt stressed, the vaccines do continue to be protective against the coronavirus.

“For folks who are concerned about breakthrough infections and whether or not vaccines are still worth it, they are absolutely still worth it,” Nesbitt said.

Following the CDC’s guidance that residents resume indoor mask wearing in parts of the country with high or substantial spread, both D.C. and Prince George’s County now have an indoor mask mandate for all individuals, regardless of vaccination status.

This story was updated to clarify DC Health Director LaQuandra Nesbitt’s comments on the rate of vaccinated people’s hospitalization from COVID-19.