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Enlarge / Crowds of people walk along the Ocean City Boardwalk during Memorial Day weekend on Sunday, May 24, 2020. (credit: Getty | Caroline Brehman)

Much about how the new coronavirus spreads from one victim to the next remains a maddening mystery. But amid all the frantic efforts to understand transmission, there is one finding that appears consistent: that it is inconsistent.

Some people—most, even—don’t spread the virus to anyone in the course of their infection. Others infect dozens at a time.

It’s a phenomenon that looked, at first, like anomalous anecdotes—a large outbreak from a Washington choir practice, a South Korean megachurch, a wedding in Jordan—but it has become a fixed feature of the new coronavirus, SARS-CoV-2. And researchers have started to settle on numbers for it.

Enlarge / Commuters wear face masks as they travel on the London Underground on June 12, 2020 as lockdown measures are eased during the novel coronavirus COVID-19 pandemic. (credit: TOLGA AKMEN/AFP)

Advice on whether or not to use face masks to limit the spread of the pandemic has varied from country to country, even differing by location within countries. These policies have had to balance whether there were sufficient supplies for medical personnel to divert some to the general public. And the whole issue was decided without a clear idea of whether face masks were actually effective against SARS-CoV-2.

But there has been reason to think masks would at least be somewhat affective, based on studies of the spread of droplets of material we expel while coughing or sneezing. And a recent analysis suggested a large group of individual studies collectively pointed to their effectiveness. But that analysis left a large degree of uncertainty about how effective they'd be at the population level and how face mask use would interact with other policy decisions.

The situation left us needing population-level modeling, which a group of UK scientists has now provided. The group's model indicates that face masks don't have to be especially effective to slow the spread of SARS-CoV-2 and can even bring benefits if they make people more vulnerable to infection. But to really control the pandemic, they will have to be combined with a lockdown if we want to see the total infected population shrink.