© (AP Photo/Vahid Salemi) A woman has her temperature checked and her hands disinfected as she enters the Palladium Shopping Center, in northern Tehran, Iran, Tuesday, March 3, 2020. Iran's supreme leader put the Islamic Republic's armed forces on alert Tuesday to assist health officials in combating the outbreak of the new coronavirus, the deadliest outside of China.

As researchers scramble to learn more about the coronavirus, which continues to spread across the globe, several questions remain unanswered.

One of those questions is, if you become infected with COVID-19 and recover, are you immune to the disease or can you be infected again?

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Here's a look at what we know so far.

Second cases reported

Last week, the Japanese government reported that a woman in her 40s, who had been working as a tour bus guide, had been re-infected with the coronavirus, testing positive after having recovered from an earlier infection.

The woman, a resident of Osaka in western Japan, first tested positive for the virus in late January but was discharged from the hospital after recovering. She tested positive again on Feb. 26 after developing a sore throat and chest pains, the government said in a statement.

The case in Japan and another similar second-positive test reported in China earlier in February have raised concerns about the recovered patient's immunity to the virus.

Stanley Perlman, a coronavirus expert at the University of Iowa told Global News that when it comes to these cases, officials need to determine whether the patients are really re-infected, or if the virus was "never really cleared" from their bodies.

Either way, Perlman says it is a "puzzling observation."

"I think either of these scenarios is a bit concerning because we would have expected the infected person to have made an immune response so that you couldn't be reinfected, certainly not two or three weeks later," he said. "On the other hand, we would have expected the virus to be completely cleared so it couldn't recrudescence two or three weeks later."

But, Florian Krammer, a virologist at the Icahn School of Medicine at Mount Sinai in New York, told the New York Times it's unlikely people are being infected for a second time.

"I'm not saying that reinfection can't occur, will never occur, but in that short time it's unlikely," he said.

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Krammer told the paper that even the mildest of infections should leave recovering patients with at least short-term immunity against the virus.

He said what is more likely to have happened is that the patients had low levels of the virus in their system when they were discharged by the hospital and that testing had failed to detect it.

Similarly, Susan Kline, an infectious disease physician, told Wired Magazine that because the outbreak has only been going on for two months, she would be "very surprised if people are getting reinfected in that time span."

Kline said she suspects the reported cases are, in fact, a "continuation of the original infection."

She said in the case of other coronaviruses that humans become infected with, patients tend to develop immunity after being sick.

The body produces antibodies to protect from subsequent exposure, Kline said.

She added that it doesn't last forever and over time the body's response wanes.

Asked how long immunity should last for those who have been infected with COVID-19 but have recovered, Perlman said it's something we don't know yet.

"We would hope those people would be protected, but we do not know," he said.

But, Perlman said in a study conducted on another human coronavirus known as Middle East Respiratory Syndrome (MERS), researchers found the antibodies were gone in as little as six months.

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What's more, Philip Tierno Jr., a professor of microbiology and pathology at New York University's School of Medicine, told Reuters that he was "not certain" the virus is not bi-phasic -- meaning it appears to go away before recurring.

"Once you have the infection, it could remain dormant and with minimal symptoms, and then you can get an exacerbation if it finds its way into the lungs," he said.

Is there a cure for COVID-19?

Bruce Ribner, a professor at the Emory University School of Medicine, told the Washington Post that when it comes to infectious diseases, there are two types of being "cured."

Ribner told the paper a patient has been "clinically cured" when they feel better and no longer show symptoms.

"Pathogen cured" refers to when doctors determine the virus is no longer in the patient's body, and that the individual can no longer transmit the disease, he said.

When it comes to COVID-19, Ribner told the Post that "we don't yet have a good handle on what it takes" for someone to be pathogen cured.

But health officials have been working tirelessly to develop a vaccine to treat the COVID-19, though it is not expected to be released for at least a year.

And last month doctors in China began using plasma containing antibodies from recovered coronavirus patients to treat those still battling the infection.

The World Health Organization on Tuesday said the virus, first detected in China's Hubei province in late December, continues to spread and has now infected more than 90,000 people in more than 70 countries, killing more than 3,100.

- With files from Reuters