A new national
study adds strong evidence that mask mandates can slow the spread of the
coronavirus, and that allowing dining at restaurants can increase cases
and deaths.
The Centers for Disease Control and Prevention released the study Friday.
“All
of this is very consistent,” CDC Director Dr. Rochelle Walensky said
during a White House briefing on Friday. “You have decreases in cases
and deaths when you wear masks, and you have increases in cases and
deaths when you have in-person restaurant dining.”
The
study was released just as some states are rescinding mask mandates and
restaurant limits. Earlier this week, Texas became the biggest state to lift its mask rule, joining a movement by many governors to loosen
COVID-19 restrictions despite pleas from health officials.
“It’s
a solid piece of work that makes the case quite strongly that in-person
dining is one of the more important things that needs to be handled if
you’re going to control the pandemic,” said William Hanage, a Harvard
University expert on disease dynamics who was not involved in the study.
The
new research builds on smaller CDC studies, including one that found
that people in 10 states who became infected in July were more likely to
have dined at a restaurant and another that found mask mandates in 10
states were associated with reductions in hospitalizations.
The
CDC researchers looked at U.S. counties placed under state-issued mask
mandates and at counties that allowed restaurant dining — both indoors
and at tables outside. The study looked at data from March through
December of last year.
The
scientists found that mask mandates were associated with reduced
coronavirus transmission, and that improvements in new cases and deaths
increased as time went on.
The
reductions in growth rates varied from half a percentage point to
nearly 2 percentage points. That may sound small, but the large number
of people involved means the impact grows with time, experts said.
“Each
day that growth rate is going down, the cumulative effect — in terms of
cases and deaths — adds up to be quite substantial,” said Gery Guy Jr.,
a CDC scientist who was the study’s lead author.
Reopening
restaurant dining was not followed by a significant increase in cases
and deaths in the first 40 days after restrictions were lifted. But
after that, there were increases of about 1 percentage point in the
growth rate of cases and — later — 2 to 3 percentage points in the
growth rate of deaths.
The
delay could be because restaurants didn’t re-open immediately and
because many customers may have been hesitant to dine in right after
restrictions were lifted, Guy said.
Also,
there’s always a lag between when people are infected and when they
become ill, and longer to when they end up in the hospital and die. In
the case of dining out, a delay in deaths can also be caused by the fact
that the diners themselves may not die, but they could get infected and
then spread it to others who get sick and die, Hanage said.
“What happens in a restaurant doesn’t stay in a restaurant,” he said.
CDC
officials stopped short of saying that on-premises dining needs to
stop. But they said if restaurants do open, they should follow as many
prevention measures as possible, like promoting outdoor dining, having
adequate indoor ventilation, masking employees and calling on customers
to wear masks whenever they aren’t eating or drinking.
The
study had limitations. For example, the researchers tried to make
calculations that accounted for other policies, such as bans on mass
gatherings or bar closures, that might influence case and death rates.
But the authors acknowledged that they couldn’t account for all possible
influences — such as school re-openings.
“It’s
always very, very hard to thoroughly nail down the causal
relationships,” Hanage said. “But when you take this gathered with all
the other stuff we know about the virus, it supports the message” of the
value of mask wearing and the peril of restaurant dining, he added.
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