A new national study adds strong evidence that wearing masks can slow the spread of coronavirus and that allowing dinner in restaurants can increase cases and deaths.
The Centers for Disease Control and Prevention released the study on Friday.
“All of this is very consistent,” said CDC director Dr. Rochelle Walensky, during a meeting at the White House on Friday. “You have decreases in cases and deaths when you wear masks, and you have increases in cases and deaths when you dine in a restaurant in person.”
The study was released at a time when some states are terminating masking mandates and restaurant boundaries. Earlier this week, Texas became the largest state to lift the mask rule, joining a move by many governors to loosen Covid-19 restrictions, despite calls from health officials.
“It’s a solid piece of work that strongly shows that dining in person is one of the most important things that needs to be addressed if you plan to control the pandemic,” said William Hanage, a Harvard University expert on disease dynamics who was not involved in the study.
The new research is based on smaller CDC studies, including one that found that people in 10 states that were infected in July were more likely to have dined at a restaurant and another that found that wearing masks in 10 states was associated reductions in hospitalizations.
CDC researchers analyzed US counties placed under state-issued masking orders and counties that allowed dinner in restaurants – both indoors and at tables outside. The study analyzed data from March to December last year.
The scientists found that the masks’ mandates were associated with reduced transmission of the coronavirus and that improvements in new cases and deaths increased over time.
The reductions in growth rates ranged from half a percentage point to almost 2 percentage points. This may seem small, but the sheer number of people involved means that the impact increases over time, experts say.
“With each day that the growth rate decreases, the cumulative effect – in terms of cases and deaths – becomes quite substantial,” said Gery Guy Jr., a CDC scientist who was the lead author of the study.
The restaurant’s reopening was not followed by a significant increase in cases and deaths in the first 40 days after the restrictions were lifted. But after that, there were increases of about 1 percentage point in the rate of growth of cases and – afterwards – of 2 to 3 percentage points in the rate of growth of deaths.
The delay may be because the restaurants did not reopen immediately and because many customers may have hesitated to dine shortly after the restrictions were lifted, Guy said.
In addition, there is always a gap between when people become infected and become sick, and even more when they end up in the hospital and die. In the case of dining out, a delay in death may also be caused by the fact that the diners themselves may not die, but may become infected and then spread to other people who get sick and die, said Hanage.
“What happens in a restaurant does not stay in a restaurant,” he said.
CDC officials have stopped saying that on-site meals need to stop. But they said that if restaurants open, they should follow as many preventive measures as possible, such as promoting outdoor dining, having adequate internal ventilation, masking employees and asking customers to wear masks whenever they are not eating or drinking.
The study had limitations. For example, the researchers tried to make calculations that took into account other policies, such as bans on mass meetings or closing bars, which could influence case and mortality rates. But the authors acknowledged that they could not explain all possible influences – such as the reopening of schools.
“It is always very, very difficult to define causal relationships completely,” said Hanage. “But when you take this along with all the other things we know about the virus, it supports the message” of the value of wearing a mask and the danger of dining in a restaurant, he added.