COVID-19: demystifying emerging reports of viral reinfection
Published:28 May 2020
CQUniversity Research Coordinator for Infectious Diseases Professor Andrew Taylor-Robinson explained that some viruses can remain ‘hidden’ in our cells.
As human beings, we are all well-equipped to fight off viruses since, as with most infectious agents, these pathogens succumb to a healthy immune system's attack – however, there are cases of viruses that lay dormant inside a person’s body, sometimes reactivating years later.
According to CQUniversity Research Coordinator for Infectious Diseases Professor Andrew Taylor-Robinson a virus can remain ‘hidden’ in our cells, sequestered away from where it can be recognised by immune defence mechanisms. The presence of this virus can be asymptomatic, meaning that we may not even have any clinical symptoms of infection. We may carry the virus but are not ill.
“Virus latency is a term used to describe the ability of a virus to lie dormant within a human host cell. This is a characteristic of certain viruses following primary infection – instead of being cleared entirely from the body virus particles can hide away from detection by the immune system for a long time, sometimes many years.”
“Reactivation of the virus occurs often following an external or environmental trigger. Once it becomes active this can result in chronic or recurrent disease,” he explained.
“A common example is Chickenpox, caused by the varicella-zoster virus. Most people are exposed to this virus as a child where they form life-long immunity so are not reinfected.
“However, in a minority of cases the virus does not disappear entirely, instead it lies dormant in the spinal column only to reactivate in adulthood as the cause of the extremely unpleasant and potentially debilitating condition shingles.
“Other notable examples are the causes of infectious mononucleosis, cytomegalovirus and Epstein-Barr virus. These are all members of the herpesvirus family.”
Viral illnesses can be caused by any of the possibly hundreds of viruses that may be circulating through a community. Our immune system, led by the production of neutralizing antibodies, provides a layer of protection against this continual exposure.
“Virus latency which leads to potential reactivation of infection should not be confused with a chronic primary infection where some may be slow to clear and for which virus may circulate in the blood for several weeks after being contracted.
“Detection of a virus is more common in the short term after exposure during the lag period which the immune system requires to make specific antibodies that will provide immunity. Once formed, those antibodies can generally last for many months, or even a few years, in the blood at recognisable levels, thereby helping to fight off potential reinfection.”
As the COVID-19 pandemic continues unabated reports are starting to emerge of individuals exposed to the causative SARS-CoV-2 coronavirus who received negative test results before testing positive weeks or, in some cases now, months later. Likewise, there are documented cases of patients who have tested positive despite having recovered from the initial infection in hospital.
“This is likely to be because some diagnostic laboratory tests detect viral nucleic acid, which may linger in the blood in trace amounts after clearance of ‘live’ virus. As methods of detection improve such anomalies of testing should decline,” Professor Taylor-Robinson explained.
For the original SARS outbreak of 2002-04 that was caused by the closely related coronavirus SARS-CoV-1, research showed that virus-specific antibodies were maintained in the blood for an average of two years.
“Reinfection with any pathogen is very unlikely while our antibodies against it are at or close to their peak levels,” he said.
“As COVID-19 is new to humans there are significant gaps in our knowledge of the natural history of infection, including the likelihood of recurrent waves of infection.
“However, it is possible that recovered patients might be susceptible to reinfection years after the initial exposure when their protective antibody response has waned. This is especially true if the virus has genetically mutated over time so that the antibodies to the first infection are less effective on subsequent exposure much like how a different strain of influenza virus circulates each year.”
While there have been over 5.5 million officially recorded clinical cases of COVID-19 worldwide, there are no confirmed cases of reoccurrence. Professor Taylor-Robinson clarified that it is still too early to tell with any certainty if someone can be reinfected.
“With the limited sample sizes available to date researchers cannot yet determine whether what appears to be a persistence of SARS-CoV-2 in the blood is due to testing inaccuracies, authentic reinfection or ‘reactivation’ of the virus, if dormancy is indeed possible.
“Additionally, there is a myriad of possible factors that may influence an individual’s incubation period with the virus, including their unique medical history and current health status, their genetic make-up and environmental stimuli.
“The many variables highlight how much we still do not know about the ‘lifecycle’ of the SARS-CoV-2 coronavirus however as more information is forthcoming the picture becomes clearer every day.”