A new CDC report shows how wearing masks and closing bars dramatically cut the rate of coronavirus infections in Arizona

• A new CDC report shows that, as Arizona closed its bars and started enforcing more mask mandates over the summer, coronavirus infection rates in the state quickly tumbled.
• It's another good signal that masks, distancing, and avoiding crowds all work really well to prevent the spread of COVID-19.
• The CDC said in its report that this "combination" approach of voluntary and mandatory disease-fighting measures "is more effective" than any one tactic taken on its own, and is especially important since we don't have a good vaccine or treatment yet.

Wear a mask and close the bars.

That's the verdict from a new report by the Centers for Disease Control and Prevention, out Tuesday, which highlights how these two actions — taken together — are critical to fighting COVID-19, the disease caused by the novel coronavirus.

The report details how both bar closures and mask mandates were likely major factors that helped rapidly slow the rampant spread of the virus across the state of Arizona after they were enacted this summer.

"Mitigation measures, including mask mandates, that are implemented and enforced statewide appear to have been effective in decreasing the spread of COVID-19 in Arizona," the report said.

Just take a look at what happened to the state's soaring coronavirus rate, after mask mandates were enacted on June 17, and bars, gyms, and movie theaters closed, on June 29:

The graph, taken from the CDC's Morbidity and Mortality Weekly Report, shows a clear pattern: the infection rate drops when people aren't spending so much time socializing indoors, are more distanced, and wear masks.

For months, public health experts have been stressing that any situation where people can exchange their spit with others — be it karaoke or a group fitness class — is a bad idea. That's the case even if no one is showing coronavirus symptoms, since some people can be infectious without ever showing signs of illness, and others often transmit their coronavirus best in the days before they feel sick.

It's not just about swapping spit, either. Sharing indoor air with someone who has the coronavirus can be dangerous too. Even the CDC now acknowledges that the virus may float further than six feet between people when it's in a poorly-ventilated space, such as a bar.

"Congregation at a bar, inside, is bad news," White House Coronavirus Task Force member Dr. Anthony Fauci told members of the US Senate in June. "We really got to stop that right now."

Fortunately, being outside, circulating fresh air (by opening a window, or improving a ventilation system), as well as the simple act of putting on a mask when you must get close to others, are all pretty effective at curbing viral spread of this respiratory pathogen.

In Arizona, the number of coronavirus cases being reported statewide decreased 75% in the period from July 13 to August 7, after bars closed, restaurants reduced capacity, and people started wearing masks.

The CDC said it's possible that other factors, including travel restrictions, individual behavior changes, and efforts to better control the virus in neighboring states might all have played a role in the decrease too.

But the agency still emphasized that "a combination of voluntary and enforceable measures" is ultimately "more effective than any single measure" taken on its own against this virus, "particularly before a vaccine or therapeutic treatment becomes widely available."

The measures the agency suggests include wearing masks, encouraging social distancing, reducing the size and number of large gatherings, working from home and staying home when possible, and pausing businesses where distance is near-impossible, like indoor bars.

As Lidia Morawska, a leading aerosol scientist in Australia, recently told Insider:

"It's not rocket science to work out what needs to be done to minimize the risk of infection."