Scientists say they've discovered that a 25-year-old man in Nevada was infected with the novel coronavirus twice, marking the first confirmed case of coronavirus reinfection in the United States, according to a case study published Monday in The Lancet.
Scientists report 1st confirmed US case of coronavirus reinfection
Mark Pandori, one of the case study's senior authors and a pathologist at the University of Nevada, Reno School of Medicine, said his team began collaborating with the Washoe County Health District early in America's coronavirus epidemic to look for possible cases of repeat infections. In June, Pandori and his team identified a Nevada man from Washoe County with "no history of clinically significant underlying conditions, and no indications of compromised immunity" who had tested positive for the novel coronavirus twice, according to the case study.
The patient first showed symptoms of Covid-19, the disease caused by the coronavirus, on March 25. His symptoms included a sore throat, cough, headache, nausea, and diarrhea. The man on April 18 underwent a reverse transcription polymerase chain reaction (RT-PCR) test for the novel coronavirus as part of a community testing event held by the Washoe County Health District. His test results were positive, and the man self-isolated.
The man's symptoms dissipated during isolation. The man reported feeling well from April 27 until May 28, and two "nucleic acid amplification tests" conducted after his symptoms had resolved came back negative for the novel coronavirus, according to the case study.
But on May 31, the patient sought care at an urgent care facility for a fever, headache, dizziness, cough, nausea, and diarrhea. Five days later, on June 5, the patient had low oxygen levels and was admitted to a hospital. While there, the man received a second RT-PCR test for the novel coronavirus, which again came back positive.
The researchers wrote in the case study that the patient's "second infection was symptomatically more severe than the first." For example, during his second infection, the patient "required ongoing oxygen support in hospital and reported symptoms that included myalgia, cough, and shortness of breath," the researchers wrote. In addition, the patient's "[c]hest radiography showed development of patchy, bilateral, interstitial opacities suggestive of viral or atypical pneumonia," the researchers reported.
On June 6, the patient underwent a serological test to determine whether he had developed antibodies against the novel coronavirus, and the test showed that he had.
The researchers discovered that the man's second coronavirus infection occurred at the same time that his parent, who lived with the man, was infected with the virus. They hypothesized that the parent's infection could have been "a possible source for secondary exposure and reinfection of [the] patient."
The researchers also performed genome sequencing on the strains of the novel coronavirus that were present in samples taken from the patient during each infection period. They determined that the viral strains were different enough that it was unlikely the man experienced "a case of continuous infection entailing deactivation and reactivation."
Case raises questions about coronavirus immunity, vaccines
Infectious disease and immunology experts say the man's case raises many questions, including how many people may have become infected with the novel coronavirus twice, how long a patient's immunity lasts after an initial infection, and why patients may experience worse symptoms during subsequent infections.
Akiko Iwasaki, an immunologist at Yale University and an investigator with the Howard Hughes Medical Institute who wrote a commentary accompanying the study, said, "There are many reasons why a person might get sicker the second time around." For instance, "[T]hey may have been exposed to a lot higher levels of the virus the second time around," or their immune response to the first infection may be making the disease symptoms worse instead of better, she said.
However, Iwasaki noted that those theories are "very speculative," because scientists don't yet have full understanding of how the novel coronavirus functions.
Researchers also have been working to understand whether exposure to the coronavirus could protect people from future infection—and for how long—which are factors that could have implications for developing a vaccine against the virus and treatments for Covid-19. However, questions regarding immunity to the novel coronavirus still haven't been answered definitively.
Danny Altmann, a professor of immunology at Imperial College London, in an email to NPR wrote that it appears about 90% of people who have experienced "a clear, symptomatic infection" from the novel coronavirus develop antibodies that prevent a second infection "perhaps for about a year." He continued, "Of course, that leaves 10% who don't" have sufficient antibodies to ward off another infection—and those people "have precisely the same risk as anyone out there, thus a small but significant number of reinfections."
According to USA Today, there have been at least 22 documented cases of coronavirus reinfection worldwide since the pandemic began, but researchers say the actual number of reinfections remains unknown.
"It could be a one in a million event, we don't know," said Iwasaki. "It's possible that the vast majority of people are completely protected from reinfection, but we're not measuring them, because they're not coming to the hospital," she explained.
Paul Offit, an infectious disease expert at Children's Hospital of Philadelphia, said he's not surprised that people could become reinfected with the novel coronavirus, because infections from similar viruses typically do not provide people with lifelong immunity.
Overall, William Schaffner, an infectious disease expert at the Vanderbilt University School of Medicine who was not involved with the Nevada patient's case, said the case should serve as "a yellow caution light," because it's too early to tell whether repeat infections are common or highly unusual.
"There's hardly an infectious disease doctor in the country who hasn't encountered a patient who thinks they've had a second [coronavirus] infection," Schaffner said. "Whether that's true or not, we don't know."
But Pandori and his colleagues in the case study raised the prospect that the Nevada man's case could have implications for potential vaccines against the novel coronavirus. If it's possible that a person could create antibodies against the virus but still not be protected against infection, that could make potential vaccines against the virus ineffective, the researchers theorized.
Iwasaki, however, said cases of reinfection have no bearing on potential coronavirus vaccines, because vaccines deliver a different type of immunity than the body. While the body's immune system can be hampered by proteins deployed by the novel coronavirus, the immune response produced by a vaccine is not as vulnerable to proteins, Iwasaki explained.
"The good thing about a vaccine is that it can induce much better immunity, a much longer lasting immunity, than the natural exposure to the virus," Iwasaki said (Weintraub, USA Today, 10/12; Hersher, NPR, 10/12; Kaplan, Los Angeles Times, 10/12; Wilde Mathews, Wall Street Journal, 10/12; Tillett et al., The Lancet, 10/12).