Can people recovering from an attack with the new coronavirus become infected again and again?
The Japanese government reported this week that a woman in Osaka had tested positive for the coronavirus for the second time, weeks after recovering from the infection and being discharged from the hospital.
Combined with China’s reports of similar cases, the case in Japan has raised some awkward questions. Reinfections are common among people who have recovered from the coronaviruses that cause the common cold.
But those pathogens are very different from the new coronavirus, and experts said it is unlikely that they will be cases of people infected a second time.
“I do not say that reinfection cannot occur, it will never occur, but in that short time it is unlikely,” said Florian Krammer, a virologist at the Icahn School of Medicine at Mount Sinai in New York.
Even the slightest infection should leave at least short-term immunity against the virus in the recovering patient, he said.
Most likely, “reinfected” patients still had low levels of the virus when they were discharged from the hospital, and the tests could not detect it.
Even if there were occasional cases of reinfection, they do not appear to be happening in numbers large enough to be a priority at this point in the outbreak.
A report published Thursday in JAMA supports the idea that people can test positive for the virus long after they appear to have recovered.
In four medical professionals exposed to the virus in Wuhan, China, the epicenter of the epidemic, a test that detects viral genetic material remained positive between five and 13 days after they were asymptomatic.
However, this does not necessarily mean that they could still infect others.
The PCR diagnostic test is highly sensitive and can amplify genetic material even from a single viral molecule. As such, the test could simply collect fragments of the virus.
The other possibility is that the negative test was performed poorly, or the samples were stored at a temperature at which the virus deteriorates. The throat swab can also ignore the virus that hides in other parts of the body.
“A virus test is positive if the virus was present in the swab in sufficient quantities at the time the sample was taken,” said Marc Lipsitch, an epidemiologist at Harvard T.H. Chan School of Public Health.
“A negative test is not definitive to know that there is no more virus in that person.”
Dr. Lipsitch offered an analogy: a jar of moldy jam on top. Scraping the surface can give the impression that the jam now has no mold, but in fact the jar may still contain mold that continues to grow.
The Japanese woman initially had mild symptoms of coronavirus infection and tested positive at the end of January. She was discharged from the hospital on February 1. She tested positive again on Wednesday after coming from a sore throat and chest pain.
“That certainly looks like it could be a real resurgence of the virus in an infectious way,” said Dr. Lipsitch. But, he added, “individual anecdotes are really hard to interpret.”
A worrying possibility is that the coronavirus follows what is known as biphasic infection: the virus persists and causes a different set of symptoms than those observed in the initial episode.
In patients infected with Ebola, the virus can persist for months in the testicles or eyes even after recovery, and It can infect others and keep the epidemic.
The recovered person may also develop other symptoms, including insomnia and neurological problems, said Angela Rasmussen, a virologist at Columbia University.
“We do not know if that is the case with this coronavirus,” said Dr. Rasmussen. “We don’t know anything about this virus.”
In general, coronaviruses are poorly understood, he said. Before the SARS epidemic, coronaviruses were not known to cause serious diseases.
Some scientists have said that people infected with the new coronavirus produce antibodies that will protect them in the future. And a single patient report suggests that immunity can last at least seven days.
But this finding is not surprising or reassuring, said Dr. Stanley Perlman, a coronavirus expert at the University of Iowa. “The problem is whether you will see it in seven months or a year,” he said. “That’s what matters to you.”
The new coronavirus closely resembles those that cause SARS and, to a lesser extent, MERS. There are no reports of reinfections with the SARS virus, said Dr. Perlman, and only one who has heard of a patient in recovery from MERS.
Dr. Perlman’s research with MERS has shown that the strength of the immune response depends on the severity of the infection, but that even in those with severe disease, which should produce the strongest immune responses, immunity seemed wane within a year.
The duration of immunity will also be a key question to solve when designing a vaccine for the new coronavirus, particularly if the virus becomes a seasonal threat such as influenza.
“What is the nature of immunity to this virus after infection?” Dr. Lipsitch said. “That is a research question that is urgent.”