Can I get the coronavirus twice?

It seems possible, though how often it happens isn’t known.

Researchers in Hong Kong recently reported evidence of a person who got the coronavirus a second time, months after an initial infection.

The finding has not yet been published in a journal. But scientists said the 33-year-old man had mild symptoms the first time and none the second time, suggesting his immune system may have provided some protection against serious illness even if it could not prevent a reinfection. His more recent infection was detected through screening and testing at the Hong Kong airport, and researchers said genetic tests revealed different strains of the virus.

Several other possible cases have been reported, including a U.S. man who was sicker the second time than the first.

Even if people can get reinfected, the World Health Organization says it likely wouldn't happen regularly.

Health experts generally believe people who had COVID-19 will have some immunity against a repeat infection. But they don’t know how much protection, or how long it would last.

This is important because if immunity wears off, it could pose a challenge for vaccines. Some experts say booster shots may be needed.

It's also unclear whether reinfected people would be able to spread the virus to others. That's another reason scientists say people should continue to wear masks, social distance and practice good hygiene.

Can I use a face shield instead of a mask?

No. Health officials don’t recommend the clear plastic barriers as a substitute for masks because of the lack of research on whether they keep an infected person from spreading viral droplets to others.

However, those who want extra protection may want to wear a face shield in addition to a mask.

Face shields have the added benefit of protecting your eyes and discouraging you from touching your face by acting as a physical barrier, says Christopher Sulmonte, project administrator of the biocontainment unit at Johns Hopkins Hospital.

Meanwhile, the available research so far indicates that the best face shields for preventing viral spread are hooded or wrap around the sides and bottom of the face, according to the U.S. Centers for Disease Control and Prevention. That’s because those shields leave less space for droplets from sneezing, coughing and talking to escape.

If you do wear a reusable face shield in addition to a mask, the CDC notes the importance of cleaning it after each use. The agency also says you should wash your hands before and after taking it off, and avoid touching your face while removing it.

Does a face mask protect me, or just the people around me?

It likely provides protection for both.

Studies on the new coronavirus and other germs show wearing a mask helps stop infected people from spreading disease to others. Evidence also suggests that masks may offer some protection for the people wearing them.

The virus spreads from droplets people spray when they cough, sneeze or talk. Surgical or cloth face masks can block most of those particles from spreading.

While some droplets may still spread out, wearing a mask could reduce the amount, providing a benefit to others. Research shows people don’t get as sick when exposed to smaller amounts of virus, said Dr. Monica Gandhi, a virus expert at University of California, San Francisco.

And masks may protect the people wearing them by reducing the amount of droplets from others that might make contact with them.

In two U.S. food processing plants where masks were required and infection clusters occurred, Gandhi noted that most workers who developed COVID-19 had mild illness or no symptoms.

Research on a different coronavirus has also found low infection rates among people who frequently wore masks in public.

Experts say masks are particularly important with the new coronavirus because infected people can be contagious even if they don’t have symptoms.

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No. While mosquitoes can spread some diseases, most notably malaria, experts say COVID-19 is not among them.

The U.S. Centers for Disease Control and Prevention says it has no data to suggest the coronavirus is spread by either mosquitoes or ticks. COVID-19 is mainly spread from person to person through droplets people spray when they talk, cough or sneeze. And the World Health Organization says a mosquito bite won’t give you the virus.

But why not, if mosquitoes can transmit other diseases? A recent study offers an explanation. Researchers say the virus would have to infect the mosquito and multiply inside of it in order for the mosquito to pass it on to people. That failed to happen when researchers injected three species of mosquitoes with the virus.

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There’s no evidence you can get COVID-19 from the water itself. But since the virus may linger on surfaces, experts say to avoid fountains if you can or to limit any direct contact when using them.

In New York City, for example, posters instruct people to use gloves or a tissue to turn on water fountains. If you don’t have those handy and need to touch the fountain, experts recommend you wash your hands afterward and avoid touching your face until you do. And you shouldn’t let your face touch the spout when leaning in for a drink.

Filling a water bottle is also better than drinking directly from the fountain, says Angela Rasmussen, a virus researcher at Columbia University. That helps ensure you don’t leave saliva on the fountain, making it safer for others.

The precautions are recommended because surfaces are believed to contribute to the spread of COVID-19, even though experts say the main way the virus spreads is through droplets people spray when they talk, cough or sneeze.

To minimize direct contact with fountains, schools and businesses should encourage everyone to bring their own water from home, says the U.S. Centers for Disease Control and Prevention. Fountains should still be cleaned and sanitized for those who need to use them, the agency says.

The CDC also says schools and businesses should check fountains for other safety issues before they reopen. Prolonged closures could increase the risk for Legionnaires’ and other diseases associated with water, since standing water in plumbing systems can cause bacteria to grow.

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Secondhand smoke isn’t believed to directly spread the virus, experts say, but infected smokers may blow droplets carrying the virus when they exhale.

Being able to smell the smoke might be a red flag that you’re standing too close to the smoker. The respiratory droplets people spray when they talk, cough or sneeze are believed to be the main way the virus spreads. And people also exhale those droplets when smoking, as well as when they’re vaping.

“Not only are they potentially spreading virus by not wearing a mask, they are blowing those droplets to the people around them to potentially get infected,” says Dr. Albert Rizzo, chief medical officer for the American Lung Association.

You should steer clear of secondhand smoke regardless. Breathing in secondhand smoke from cigarettes can cause various health problems, according to the U.S. Centers for Disease Control and Prevention.

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Yes, it’s possible.

The World Health Organization recently acknowledged the possibility that COVID-19 might be spread in the air under certain conditions.

Recent COVID-19 outbreaks in crowded indoor settings — restaurants, nightclubs and choir practices — suggest the virus can hang around in the air long enough to potentially infect others if social distancing measures are not strictly enforced.

Experts say the lack of ventilation in these situations is thought to have contributed to spread, and might have allowed the virus to linger in the air longer than normal.

In a report published in May, researchers found that talking produced respiratory droplets that could remain in the air in a closed environment for about eight to 14 minutes.

The WHO says those most at risk from airborne spread are doctors and nurses who perform specialized procedures such as inserting a breathing tube or putting patients on a ventilator. Medical authorities recommend the use of protective masks and other equipment when doing such procedures.

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It doesn’t seem to have changed in a way that makes people less or more sick. There’s some evidence that a specific mutation called D614G may have made it easier for the virus to be transmitted between people. But not all scientists are convinced, and it’s hard to say how strong any such effect might be.

The D614G mutation, which appeared quite early in the pandemic, has since become so common that most outbreaks are caused by strains that carry it.

It’s normal for viruses to mutate over time, but most genetic changes don’t affect their behavior.

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The AP is answering your questions about the coronavirus in this series. Submit them at: FactCheck@AP.org.

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