There’s probably no need to disinfect your groceries or pull on a pair of sterile gloves to open your mail. Wearing a mask to an outdoor event is an effective way to protect yourself and others. But lingering indoors, inside a crowded bar without wearing a mask, is almost a surefire way to pass the coronavirus.

This is what scientists are learning about the transmission of COVID-19 six months after it was first identified and as society attempts to reopen amid a pandemic that kills hundreds and infects tens of thousands daily in the United States alone.

A microscopic view of the coronavirus. creativeneko/Shutterstock.com

It’s still too early to draw final conclusions, but there has been little evidence to date of disease outbreaks in the wake of racial injustice protests across the U.S. in which many participants wore masks. On the other hand, the reopening of bars and restaurants in a number of states in the South and West have been linked to a number of outbreaks – often involving younger people.

Maine has experienced lower infection rates than most states, and while some states are experiencing a surge in cases and hospitalizations, Maine’s virus cases are on a downward trajectory as testing continues to ramp up. But that doesn’t mean the virus is gone in Maine or is no longer a threat.

Dr. Nirav Shah, director of the Maine Center for Disease Control and Prevention, has said repeatedly that Maine needs to “keep our collective feet on the gas pedal” to keep a lid on the spread of the virus, especially as tourism season unfolds and more visitors arrive. Although those age 60 and older are most at risk of dying from COVID-19, younger people are not immune, and can contract and transmit the virus.

Many unknowns remain, but consensus on transmission of the virus, and how to minimize it, is emerging.

Masks stop virus’ spread

Scientists provided conflicting studies and advice early in the pandemic, but research is now firmly on the side of mask-wearing to stop the spread of the virus, especially indoors in public places, health experts say. The shift from conflicting advice to consensus came about as scientists learned more about the virus and how it is spread.

One of the more definitive studies examined the impact of wearing masks in outbreak areas in Wuhan, China, Italy and New York City.

A sign at the entrance to the Hannaford supermarket in Scarborough on Friday, March 27, 2020 reminds customers to stay six feet apart while in the store. Staff photo by Gregory Rec

“Our analysis reveals that the difference with and without mandated face covering represents the determinant in shaping the trends of the pandemic,” according to research published in the June 10 editions of the Proceedings of the National Academy of Sciences. “This protective measure significantly reduces the number of infections. Other mitigation measures, such as social distancing implemented in the United States, are insufficient by themselves in protecting the public.”

Masks work by preventing the spread of droplets through the air from one person to another – such as from sneezing and coughing. Many with COVID-19 are most contagious before they experience symptoms, which is one reason why the novel coronavirus is so difficult to contain. That’s different from influenza. Typically, people who have the flu are most contagious at the same time they are feeling ill and likely to stay home.

The U.S. Centers for Disease Control and Prevention says coronavirus transmission is more likely when someone has “close contact,” defined as spending 15 minutes or more within 6 feet of an infected person, beginning two days before they got sick or two days before an asymptomatic person was tested. Close contact in confined spaces raises the risk, although it’s not clear how much the risk declines if close contact is more fleeting.

Jennifer Kates, senior vice president and director of global health and HIV policy for the Kaiser Family Foundation, a national health policy think tank, said wearing masks is crucial, especially indoors.

“There are a lot of people walking around who don’t know that they’re infected, and there’s so much asymptomatic spread, so if we all just wear masks, it’s really key. The data are clearer and clearer on the importance of masks.”

Maine requires people to wear masks indoors or in outdoor settings where physical distancing is impractical, and mandates that store owners post signs informing customers of the mask requirements. Compliance, however, varies greatly from community to community, or even store to store.

Surfaces not as big a concern

At the beginning of the pandemic in the United States this spring, scientists were warning about the virus living on surfaces and the potential for transmission from surfaces to people.

Some people were disinfecting grocery bags or wearing surgical gloves to play a game of catch.

Postal carrier John Graham delivers mail in North Deering in April. Staff photo by Ben McCanna

But Kates said that after months of research, there’s a lot less concern about virus transmission from surfaces to people. If the virus lives on a surface, it’s likely in such a weakened state that it can’t cause an infection in a person.

“The primary way people are infected is by other people,” Kates said. “I’m not worried about a ball transmitting the virus.”

Kates said, however, that practicing good hygiene – by washing hands frequently after touching common surfaces, such as door handles at a hotel – will help people avoid the the novel coronavirus and other bacteria and viruses.

The U.S. CDC website says the virus can live on surfaces, but surfaces are not the primary way the virus is transmitted.

“There’s a long chain of events that would need to happen for someone to become infected through contact with groceries, mail, takeout containers or other surfaces,” Dr. Julie Marcus, an infectious disease epidemiologist and assistant professor at the Harvard Medical School, told the New York Times in a May 28 article.

Virus disperses more quickly outdoors

When measuring the risk of any activity, one of the main questions to ask is whether the activity is outdoors or indoors. The virus disperses much more quickly in outdoor settings.

Meanwhile, research is finding much higher transmission rates at indoor events. Studies of an indoor choir practice in Washington state, and outbreaks at bars in South Korea, Idaho and Florida, show the potential for exponential spread in indoor settings, especially where people are without masks, talking loudly or singing close to one another.

Bars and other indoor settings where large numbers of people gather without masks are the prime conditions for exponential growth, said William Hanage, associate professor of epidemiology at Harvard University.

“We, as a people, have underestimated this virus,” Hanage said in a conference call with reporters this week. “If you offer the virus sufficient opportunities to transmit, then it will take them.”

Texas shut down bars on Friday after the state experienced a surge in cases, and Boise, Idaho, also shut down bars this week after dozens of cases were linked to bars in the city’s downtown.

The Mills administration indefinitely delayed indoor bar service that was set to open July 1 after noting the high transmission at bars in other states.

Scientists are also looking at the recent Black Lives Matter protests, but so far there is not a connection between the protests and virus spread.

Barry Bloom, research professor of public health at Harvard University, said in a conference call with reporters that the protests are so recent that the science needs time to catch up, but he said mask wearing and the protests being outdoors helped mitigate the spread of the virus.

“It’s probably too early to ask the question to what extent the Black Lives Matter protests in 315 cities and towns have had on transmission,” Bloom said. “The good news is they were outdoors.” No cases in Maine have yet been linked to protests, but Shah has noted that it’s too early to draw conclusions.

In general, Kates said, gathering outdoors at least 6 feet away from people is much less risky than congregate settings indoors.

Optimism for children and schools

The research is not definitive, but some studies point to children – especially those younger than middle school age – being not only less likely to contract COVID-19, but even if they have the virus are perhaps less likely to spread it to others.

Hanage said that bodes well for schools reopening, but the older the students are, the more transmission is similar to adults, so he advises schools to be most cautious with high school or college students.

“There is some reason for cautious optimism, but it’s not necessarily a reason to throw the schools open,” Hanage said.

If incidence of the disease remains low in the community – like it has so far in Maine – then schools can be more confident that they will not be vectors of the disease, Hanage said.

“When community transmission is higher, that would impede our ability to open schools,” Hanage said. “We should want to give higher priorities to schools. We should be asking which things do we want to reopen? I would far rather see a school open than a casino.”

Kates said it’s not just schools reopening, but what types of activities within the schools should be allowed to happen. If schools need to shut down band and choir practice, contact sports and indoor sports until 2021, that may be necessary so that schools can stay open and avoid a late fall “second wave,” Kates said.

“Contact sports and indoor sports are much higher risk and probably would not be activities that would be recommended,” Kates said. “If these risky activities lead to transmission in a school then you might have to close the whole school down.”

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