US health authorities now recommend people wear face protection to lessen the risk of spreading the new coronavirus.

Relatively early in the coronavirus outbreak, many experts thought that people who clearly showed COVID-19 symptoms—coughing, sneezing, fever, and breathing problems—were the ones most likely to spread the disease. On January 28, Anthony Fauci, the head of the National Institute of Allergy and Infectious Diseases and one of the most prominent faces of the US government pandemic response said, “the driver of outbreaks is always a symptomatic person, even if there’s a rare asymptomatic person that might transmit.” Three days later, Fauci had an updated message: “In the beginning we were not sure if there were asymptomatic infection[s], which would make it a much broader outbreak than what we’re seeing. Now we know for sure that there are.”

A seemingly constant feature of the outbreak has been the need for health experts to regularly re-evaluate their understanding of the coronavirus. Here are three questions where at least a little uncertainty remains:

Will the outbreak ease over the summer? Ever since the first cases of COVID-19 were reported in Wuhan, China, many have held out hope that warmer weather would eventually bring some reprieve and suppress the spread of the new virus. Fauci, for instance, told NPR recently, “We hope we get a respite as we get into April, May, and June.” While Fauci emphasized that it’s not clear whether the outbreak would ease when the weather warmed, past outbreaks offer some precedents for such a pattern. The first cases of another coronavirus-caused disease, severe acute respiratory syndrome, or SARS, were reported in China in November 2002. By July of the following year, the World Health Organization declared the deadly outbreak contained.

But Harvard epidemiologist Marc Lipsitch warned in a blog post against thinking warmer weather will necessarily bring about the end of COVID-19. “SARS did not die of natural causes. It was killed by extremely intense public health interventions in mainland Chinese cities, Hong Kong, Vietnam, Thailand, Canada, and elsewhere,” Lipsitch wrote.

The spread of other coronaviruses, like the ones that can cause common colds, tends to die down in the warmer months. The same is the case for influenza. But whether the new coronavirus will follow that pattern remains a question. Because this new coronavirus just began to infect humans, many people haven’t developed immunity to it. So even if there are seasonal variations in how easily the new coronavirus transmits among humans, it may still infect some of them, offseason.

“For the novel coronavirus SARS-CoV-2, we have reason to expect that like other betacoronaviruses, it may transmit somewhat more efficiently in winter than summer,” Lipsitch writes. He expects a “modest” change in transmission in the northern hemisphere, as warmer weather arrives there.

Should you wear a mask? On Feb. 29, US Surgeon General Jerome Adams implored people not to buy up the masks that health care workers needed, tweeting, “Seriously people- STOP BUYING MASKS!” The Centers for Disease Control and Prevention (CDC) didn’t recommend that the general public wear them. But the official guidance from the agency has changed, and now people are encouraged to wear fabric masks that may offer some protection and won’t diminish the supply of surgical masks that health care workers need.

Seriously people- STOP BUYING MASKS! They are NOT effective in preventing general public from catching #Coronavirus, but if healthcare providers can’t get them to care for sick patients, it puts them and our communities at risk!

https://t.co/UxZRwxxKL9 — U.S. Surgeon General (@Surgeon_General) February 29, 2020

The agency said it’s updating its policy because a clearer picture is emerging about how people who may not appear sick can still spread the coronavirus.

CDC director Robert Redfield recently told NPR that perhaps 25 percent of infected people are asymptomatic. (The World Health Organization, meanwhile, considers truly asymptomatic cases to be rare, according to one of its reports from February. Most people who don’t show symptoms during a test eventually will, the report suggests.) What appears to be fairly common, however, are cases of pre-symptomatic people who still spread the disease.

A study in Singapore found that of 157 people who contracted the disease locally between January 23 and March 16, 10 were infected by a so-called source patient who did not have symptoms at the time. People can spread COVID-19 up to three days before they show symptoms, the study found. That means a strategy built around isolating sick patients to stop the spread has real limitations, one factor in the changing guidance from US health authorities on whether the general public should wear masks or not.

The debate over masks has been a fiery one in the United States, and CNN reported that some at the CDC felt “pressured” into updating the agency’s guidance. Some public health experts worry that masks will lull people into a false sense of security in return for only modest benefits.

While they agree that people will still have to remain vigilant about keeping apart from others, other experts believe the protection masks can offer is important.

Is food safe? Many food scientists agree with the US Food and Drug Administration assessment that food is not a known pathway for getting COVID-19. At the same time, a growing body of research is showing that coronavirus can cause digestive symptoms and that feces can contain the virus, raising questions for many researchers about whether there could be a fecal-oral transmission route.

People can get sick from germs like norovirus or hepatitis A after consuming food contaminated with feces, often because someone handling the food didn’t wash his or her hands properly. COVID-19 is a respiratory disease and inhaling the virus is widely viewed as the primary route of infection. According to a March 29 World Health Organization document, there “have been no reports of [fecal]−oral transmission of the COVID-19 virus.” Likewise, the US Food and Drug Administration says, “Foodborne exposure to this virus is not known to be a route of transmission.”

The World Health Organization did note in a 2008 report that SARS-CoV, the coronavirus that causes SARS, while primarily infecting people via airborne pathways, “may occasionally be transmitted via food.”

A US Environmental Protection Agency chemist who temporarily lost her job after correctly reporting that the 9/11 terrorist attacks had released hazardous dust into lower Manhattan recently sent an email to her agency colleagues that argues the federal government is downplaying the risks of contracting COVID-19 through food. “Everyone appears to quietly recognize the potential for fecal contamination to the mouth leading to [coronavirus] transmission,” Cate Jenkins, the agency chemist, told the Bulletin. “But if you grant that hypothesis, food could well be contaminated by fecal matter, and/or droplets from a cough, sneeze or simply talking.”

In an interview with the Bulletin, a professor in Rutgers University’s Department of Food Science, Donald Schaffner, said it’s possible that COVID-19 could be spread by food, but there is no evidence for that mode of transmission. Furthermore, Schaffner said, people have little choice but to eat. The biggest risk that COVID-19 poses to the food system, Schaffner said, is that food workers could get sick and not be able to work. “I guess there’s a theoretical chance they could contaminate food,” he said. “But more importantly, they’re going to stop working, which is going to make it harder for us to get the food that we need.”

But given the breakneck pace of research on and changes in knowledge about this coronavirus, Schaffner wanted to qualify his views: “Let’s time stamp this conversation, right? We’re talking Saturday, April 4.”

Our understanding of the new coronavirus pandemic is anything but complete. “The world,” Schaffner noted, “is changing quickly.”