Mandating mask wearing last year appeared to slow the spread of COVID-19 while lifting indoor dining restrictions seemed to accelerate it, a new study by the Centers for Disease Control and Prevention says.

The findings further validate the argument that states should not yet be easing public health measures, federal officials said Friday. 

The study appears in the latest CDC Morbidity and Mortality Weekly Report. It tracked county-level data from March 1-Dec. 31 of last year and found decreases in the growth rates of daily COVID-19 cases and deaths within 20 days after mask mandates were implemented. 

The analysis also found that growth rates began to increase 41 days after restrictions on on-premises restaurant dining were lifted. 

The study comes days after Texas and Mississippi announced they were ending statewide mask mandates and capacity limits on businesses. 

CDC Director Dr. Rochelle Walensky said the study “serves as a warning about prematurely lifting these prevention measures.”

“I know the idea of relaxing mask wearing and getting back to everyday activities is appealing, but we're not there yet,” she said. “And we have seen this movie before. When prevention measures like mask mandates are rolled back, cases go up.”

The study found that 1-20 days after the mask mandates began, the growth rate declined by 0.5 percentage points. From 81-100 days, the growth rate fell by 1.8 percentage points. The growth rate of deaths decreased by as much as 1.9 percentage points.

The growth rate of COVID-19 cases increased by as much as 1.2 percentage points 41-100 days after indoor dining resumed, and the growth rate of deaths increased by as much as 3 percentage points.

Walensky also said Friday that the decline in coronavirus cases and deaths has plateaued. The seven-day average for new cases stands at 62,555, while the seven-day deaths average is 1,921.

“The current numbers concerning cases and deaths are still too high,” the CDC director said.

Health officials did not advocate Friday for closing restaurants, but rather urged Americans to continue wearing masks and socially distancing.  

“It may seem tempting in the face of all of this progress to try to rush back to normalcy as if the virus is in the rearview mirror. It’s not,” said Andy Slavitt, White House senior adviser for COVID-19 response. "Now years of watching football on TV have shown me that it's better to spike the football once you're safely in the end zone, not after you've made a couple of completions.” 

Walensky added the CDC will “soon” release its guidance for fully vaccinated people and activities they can resume.