A new case study, from scientists at the University of Hong Kong, is reporting the first clinically confirmed case of SARS-CoV-2 re-infection. Responding to the news, a variety of infectious disease specialists suggest the re-infection is not necessarily surprising, could be rare, and may have implications for the efficacy of a vaccine, but many unanswered questions still remain.
More than six months into this global pandemic, scientists are only now beginning to glean insights into the longer-term characteristics of this novel coronavirus. One of the key questions yet to be resolved is whether a person can contract COVID-19 a second time.
Recent studies have begun to indicate certain markers of immunity may start to wane in the months following a primary infection. Anecdotally there have been numerous stories of individuals testing positive for the virus weeks, and sometimes even months, after recovering from the disease.
Many of these secondary positive cases are thought to be due to remnants of the virus still present months later. These cases are not new infections, but instead more likely lingering residual signs of the initial infection, and experts suggest these viral remnants cannot infect others.
The important detail in this new case study, accepted but not yet published in the journal Clinical Infectious Diseases, is it offers the first robust clinical evidence of an entirely new, secondary infection, months after the subject recovered from their initial infection.
The report outlines the case of a healthy 33-year-old Hong Kong man. He suffered his first SARS-CoV-2 infection in late March. The primary infection was relatively mild, with the patient suffering standard COVID-19 symptoms: cough, fever, headache, and sore throat.
By mid-April the man tested negative for SARS-CoV-2. Months later the man arrived back in Hong Kong after travels to Europe. Routine testing upon arrival at Hong Kong airport revealed the man was again positive with SARS-CoV-2. However, this time he remained entirely asymptomatic, with no fever or abnormal signs whatsoever.
Genomic testing revealed the new infection was an entirely different strain of the virus, offering the first documented evidence of a SARS-CoV-2 re-infection.
The case study raises a whole host of questions that currently have no good answers. Perhaps the most pressing question raised by the new report is exactly how infectious is an individual during a second COVID-19 episode?
“Given the number of global infections to date, seeing one case of reinfection is not that surprising even if it is a very rare occurrence,” says Jeffrey Barrett, from the COVID-19 Genome Project at the Wellcome Sanger Institute. “This may be very rare, and it may be that second infections, when they do occur, are not serious (though we don’t know whether this person was infectious during their second episode).”
Paul Hunter, from the University of East Anglia, echoes Barrett’s comments, saying it’s unclear exactly how much of a risk to others this kind of second infection may be. Being the first documented case study of its kind, there is currently no information comparing the viral load of a first infection to a second. Hunter does note the asymptomatic nature of this secondary infection suggests the disease could be milder in a second episode.
“It is quite likely that subsequent infections do not cause as severe an illness as the first episode because of some degree of residual immunity which may not be sufficient to stop the infection but be enough to reduce the risk of severe illness,” says Hunter.
David Strain, from the University of Exeter, is a little more concerned about this new report. He says the study could be an early warning that vaccines may struggle in corralling the spread of COVID-19.
“… [The report] raises the possibility that vaccinations may not provide the hope that we have been waiting for,” says Strain. “Vaccinations work by simulating infection to the body, thereby allowing the body to develop antibodies. If antibodies don’t provide lasting protection, we will need to revert to a strategy of viral near-elimination in order to return to a more normal life.”
Brendan Wren, from the London School of Hygiene and Tropical Medicine, on the other hand is not at all surprised by this report. He points out viruses naturally mutate all the time, so this case of reinfection is not unusual, may be rare, and shouldn't influence the development of vaccines.
“It is to be expected that the virus will naturally mutate over time,” says Wren. “This is a very rare example of re-infection and it should not negate the global drive to develop COVID-19 vaccines.”
Perhaps the clearest takeaway from this new report is that the potential for re-infection means those who have already recovered from COVID-19 should be vigilant in their social distancing and mask-wearing practices. In a statement from the Hong Kong research team it's also suggested once an effective vaccine is established it should be administered to those who have previously contracted the virus.
“Our findings suggest that SARS-CoV-2 may persist in the global human population as is the case for other common-cold associated human coronaviruses, even if, patients have acquired immunity via natural infection,” the researchers write in a statement. “Since the immunity can be short lasting after natural infection, vaccination should also be considered for those with one episode of infection. Patients with previous COVID-19 infection should also comply with epidemiological control measures such as universal masking and social distancing.”
A PDF of the new report can be found here (via Ars Technica).
