Catching COVID-19 Again – Once Bitten, Twice Shy

Amid all the speculations about so-called “herd immunity,” the jury is still out on reinfection with COVID-19.

Catching COVID-19 a second time would look like this: An individual tests positive for the virus and symptoms of the disease, recovers and tests negative. Sometime later, after recuperating, the symptoms return, and the test becomes positive again. If the test results are reliable – no false positives or negatives – this means reinfection with SARS-CoV-2. 

So far, this situation is rare: There are only a few reports of people who seemed to have caught COVID-19 a second time, and not enough knowledge and experience with SARS-CoV-2 to figure out whether being re-infected is common or not. 

The main concern of a repeat recurrence of COVID-19 is that it means that natural infection might not induce lifelong immunity, which makes developing a vaccine and establishing herd immunity more challenging than we thought. 

Lessons from Other Viruses

Is there a precedent? Sadly, yes. There is a spectrum of responses to viruses like measles, mumps, chickenpox, herpes, HIV, Dengue, influenza and viruses that cause the common cold and intestinal infections. Viruses induce different types of diseases and immune responses . 

Some viruses lead to long-term immunity, like with measles – meaning that you typically will not catch it again. Some viruses have short-term immunity which means that you can get infected repeatedly, as with the common cold. With Dengue virus, an infection makes you more susceptible to a second infection, while chickenpox and herpes viruses live in the body forever. They can reactivate to cause illness – as with shingles later in life. . HIV also lives in the body forever. 

All these viruses have one thing in common – we know a lot about them because we’ve studied them for decades. 

Immunity and COVID-19 

Can we use this knowledge to help us understand immunity to SARS-CoV-2? Yes, but we need to know more about this particular virus to predict how everyone will respond to it, and what the characteristics of reinfection are. For example, reinfection could cause a milder disease than the first infection or be less contagious. Or vice versa. 

As we learn more about COVID-19, we are starting to get an immunity picture, but there is still a lot to figure out. Many SARS-CoV-2 infected people produce protective, neutralizing antibodies and some mount cell-mediated immune responses with SARS-CoV-2-specific T lymphocytes. The goal of these responses is to kill the virus and allow people to recover from the infection. 

We hope that the majority of patients will recuperate with high levels of antibodies and protective cells, so that reinfection is not possible – that the virus doesn’t hide in the body and reactivate or re-infect to cause disease again. 

Immunity and Reinfection 

Prolonged production of neutralizing antibodies and cellular responses against SARS-CoV-2 could protect against reinfection, but it’s not clear whether all people respond in the same way and whether the protection lasts. 

Antibodies seem to be higher in people who were severely ill compared to those with mild symptoms, and lead to immunity in animals in short-term experiments. But it’s looking more and more as if immunity disappears over time, as it does for the common cold. Without long-lived immunity, reinfection with SARS-CoV-2 and catching COVID-19 again is possible. 

More Time and More Research

We need more time and more research to understand immunity after natural infection and vaccination. We have had decades to understand the patterns of other viruses, but only a few months to understand the long-term effects and potential for reinfection for SARS-CoV-2. 

To establish a pattern, we need to characterize the patients that produced protective antibodies and cellular responses. Are they old, young, female, male, severely ill or mildly ill patients or have pre-existing conditions that influence immunity? Also, we need to determine how long protection lasts after infection and vaccination by screening those recovered to identify the risk of reinfection. 

The main aim now is to continue rapidly analyzing the data with the intention of directing the design of a highly protective vaccine that stimulates lasting and robust immunity against the SARS-CoV-2 virus. 

Protection Against Reinfection

Until we’ve figured it out – even if you’ve had COVID-19 – you must do what ‘never infected’ people are doing to curb the spread of the virus: Reduce social interactions and when you do get together with others, continue social distancing, mask-wearing, hand-washing, cleaning frequently touched surfaces, covering your mouth and nose when coughing or sneezing, and by all means, avoid touching your face.  

Dr. Michelle Epstein
Michelle Epstein is a medical doctor graduated from the University of Alberta in Canada, who has specialised in Internal Medicine at the University of British Columbia and Allergy and Clinical Immunology at Yale University. Since 2004, she has been a Lab Leader at the Medical University of Vienna’s Division of Immunology.

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