As the weather turns colder this fall and Mainers head indoors, public health experts are bracing for an increase in COVID-19 infections, with people sharing closed spaces where the virus spreads more easily.

But after more than six months of studying COVID-19, which had infected 28 million people globally by Saturday, scientists are making new discoveries about the disease. Some of those discoveries could help Mainers do a better job of protecting themselves from the virus.

Among the latest findings:

• Research shows that one way to reduce risk is to find buildings with good ventilation, if possible, to minimize COVID-19 exposure.

• Keep wearing a mask. Scientists have learned that wearing a mask provides even more benefits than originally thought and that a mask may actually protect the wearer from exposure.

• The intensity of exposure to infected respiratory droplets could determine whether you have a mild or severe case of COVID-19.

• For those who do get sick, research suggests that natural immunity likely lasts months or longer, and that reinfections are extremely rare. And doctors are gaining knowledge about how to treat the virus more effectively.

The coronavirus has upended society, closing schools and businesses and altering patterns of life while causing more than 193,000 deaths in the United States, including 135 in Maine as of Saturday. But scientists continue to work on many aspects of the disease to learn how the virus attacks the body, what treatments may work, vaccine development and what steps we can take as a society to reduce the harm caused by the virus.

Here’s some of what we’ve learned so far.

NATURAL IMMUNITY

For those who do contract COVID-19, how long does natural immunity last? Weeks, months, years or perhaps lifetime immunity?

Science does not yet have a definitive answer on this, but Dr. Meghan May, a virologist with the University of New England, said she is optimistic natural immunity would be long-lasting, for similar reasons that a vaccine should be effective. When a virus is slow to mutate, that gives the body’s immune system better tools to fight off future introductions of the virus.

May said it’s difficult to say for sure, but “there’s every reason to expect becoming infected should give you good protection.” How long is unknown, because the virus has been circulating in humans for less than a year. One of the most similar viruses to COVID-19 – SARS – had an outbreak in the early 2000s but then fizzled out, which meant scientists didn’t get a chance to find out how long natural immunity to SARS lasted.

Still, May said she would lean more toward a longer-lasting immunity because the virus is slow to mutate.

The sluggish pace of mutation in the novel coronavirus also means a vaccine is more likely to be effective at preventing the virus and offer longer-term protection. May said it’s difficult to know right now, but the vaccine could be as effective as the chickenpox or measles vaccines, which offer widespread protection.

Although reinfection stories have made the news recently, May said the fact that reinfections are extremely rare means that it’s not likely to be a widespread problem.

“We’re talking about a number of reinfection cases that’s less than one hand,” May said. “Considering the millions of humans on this planet who have gotten COVID-19, that’s actually kind of encouraging. It kind of tells us reinfection really isn’t a big problem.”

A strategy that’s being floated by the Trump administration – letting the virus spread unfettered to achieve “herd immunity” in the population – has been denounced by most public health experts.

Doing so could result in millions of additional deaths in the United States, on top of the 190,000 who have already died from COVID-19.

“Herd immunity would be difficult to achieve with this virus,” said Dr. James Jarvis, medical specialist for Northern Light Health. “The health care system would be overwhelmed. We would have a high mortality rate, high levels of severe disease. We would not want that to be a solution to this problem.”

MASKS

Masks continue to shine as an effective tool against COVID-19, according to a number of studies. Some recent studies even suggest that masks may protect the wearer.

If you wear a mask and have COVID-19, it will likely prevent others from getting sick. Since people are most contagious in the early stages of the disease – often before people develop symptoms – people don’t know that they are sick, which makes masks crucial in preventing the spread. About 40 percent of transmission occurs from pre-symptomatic or asymptomatic people with COVID-19, according to the U.S. Centers for Disease Control and Prevention.

According to a review of 115 studies by Brigham Young University, “masks prevent infected people from spreading the virus to others by trapping the respiratory droplets (tiny moisture particles) that are produced when we cough, speak, and breathe. Cloth masks can stop 90 percent or more of the dispersal of droplets carrying the virus.”

In a Chinese study involving hamsters, scientists found that masks may help the wearer be less exposed to the virus because the mask may stop some of the virus from reaching the face.

“Without more research, we can’t be certain that masks protect the wearer. But we do know they don’t hurt, and that they protect others,” according to Harvard University’s Coronavirus Resource Center.

The type of mask worn also makes a difference. The most effective are N-95 masks, followed by cloth and surgical masks. Least effective are neck gaiters and bandanas.

According to a New York Times analysis in July of mask compliance across the country by ZIP code, on average 59 percent of Americans wear masks. In Maine, mask compliance varies widely, with the Portland area and the midcoast reporting mask compliance around 70 percent or more, while rural areas had mask compliance levels of about 40 percent.

VIRAL LOAD

Studies of mask wearing may also be shedding light on another phenomenon – how the “viral load” of someone with COVID-19 that you are exposed to may reduce the severity of disease if you do contract COVID-19.

When comparing disease spread on two cruise ships – one where masks were issued after a single case of COVID-19 was discovered, and one where it wasn’t, the differences are staggering.

According to a March study published in the National Center for Biotechnology Information scholarly journal, on the Diamond Princess cruise ship docked in February in Japan, where masks were not routinely distributed, 18 percent of 631 passengers who tested positive for COVID-19 were asymptomatic. In March, an Argentinian cruise ship distributed masks to cruise-goers after one positive case, and 81 percent of the 128 who tested positive were asymptomatic, according to a study in the British Medical Journal, suggesting that mask-wearing reduced the severity of the disease.

Dr. Monica Gandhi, an infectious-disease specialist at the University of California San Francisco, told an internal university publication in July that the cruise ship comparison also indicates that viral loads may play a role in how sick you get when exposed to the virus. Wearing a mask may reduce the number of infected particles if you are exposed to someone with COVID-19. Research on that topic is in the early stages.

“Masks, which filter out a majority of viral particles, can lead to a less severe infection if you do get one,” Gandhi said. “If you get infected, but have no symptoms, that’s the best way you can ever get a virus.”

VENTILATION 

Joseph Allen, associate professor of exposure assessment science at Harvard University, wrote a guide for how buildings can be ventilated to help reduce the spread of COVID-19.

“I am not talking about advanced ventilation systems that are very expensive,” Allen said. “We are talking about practical, inexpensive steps that can be implemented in nearly every building right away. Even cracking a window open six inches can really help.”

Scientific studies are pointing to ventilation as an important way to reduce the chances of COVID-19 spreading when meeting outdoors becomes impractical, as in winter. According to a study published in July in The Lancet medical journal, “improving ventilation of public spaces will dilute and clear out potentially infectious aerosols.”

In the study, researchers “analyzed the number of droplets passing through the stationary laser sheet suspended in the center of the experimental chamber. We repeated this experiment in three rooms with different levels of ventilation: no ventilation, mechanical ventilation only, and mechanical ventilation supported by the opening of an entrance door and a small window. In the best-ventilated room, after 30 (seconds) the number of droplets had halved, whereas with no ventilation this took about 5 (minutes). In a poorly ventilated room, the number of droplets was halved in 1-4 minutes.”

Ventilation is an issue rapidly coming up for schools, as despite efforts to expand outdoor learning spaces, students will have to be indoors at times.

CHILDREN

The idea that children may be less likely to transmit COVID-19 even if they are carriers was suggested in studies this spring. However, that may not be holding up. A South Korean study published in July of more than 5,700 children showed that children ages 10 and over are just as likely to transmit the virus as adults. Children under age 5 may have between 10 and 100 times the “viral load” as adults, suggesting they may be more likely to transmit the disease, according to a study by the Lurie Children’s Hospital of Chicago.

What is known, Allen said, is that tools used to reduce the spread, such as wearing masks, keeping physically distant, improving ventilation and limiting the number of people in a building, are effective. For instance, a U.S. CDC study of four summer camps in Maine where strict protocols were followed meant there was only a handful of cases out of more than 1,000 staffers and campers. But at other summer camps where protocols were not followed, COVID-19 spread rapidly.

“We are thinking about risk in a very narrow sense of virus exposure in the classroom, but there’s risk of having devastating consequences of keeping kids out of schools,” Allen said. “Next year’s headlines are going to be about consequences of dropouts, abuse and neglect. These stories are hidden by view for now.”

TREATMENTS

While there is no cure yet for COVID-19, scientists have been working on a number of treatments.

The World Health Organization recently recommended using steroids for severely ill patients who are hospitalized, noting that several studies conclude using the steroids, which are inexpensive and widely available, can reduce deaths by about 30 percent.

The WHO analyzed seven separate studies and concluded that a certain type of steroids – corticosteroids – should be standard care for patients with “severe and critical” COVID-19.

“Administration of steroids is clearly associated with benefit among critically ill patients with COVID-19, although the exact threshold at which an individual patient should be prescribed corticosteroids remains unclear,” said Dr. Hallie Prescott and Dr.Todd Rice, professors of medicine at the University of Michigan and Vanderbilt University, in an op-ed published in the JAMA scholarly journal. The steroids “should be first-line treatment for critically ill patients with COVID-19.”

Maine Medical Center Research Institute has been participating in some of the national clinical trials for treatments, including a high-profile study of remdesivir, an anti-viral drug that can help stop the virus from replicating.

Remdesivir has been shown to have modest benefits for people with severe disease, reducing hospital stays.

Dr. Dan Meyer, Maine Med’s director of hospital medicine, said other research trials involving Maine Med include the effectiveness of anti-inflammatory drugs with patients with severe diseases, and whether blood thinners should be part of routine treatments for patients, who often suffer from blood clots.

“The medical community is trying to answer the question whether administering the blood thinner even in the absence of a clot improves outcomes for patients,” Meyer said.

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