COVID-19 Reinfection: What to Know

Medically Reviewed By William C. Lloyd III, MD, FACS
 young female nurse wearing surgical mask takes temperature of masked white male in his forties in an examination room of a medical clinic
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How many times can you get sick with COVID-19? That’s a question many people—and researchers—want to know the answer to. But, answers remain elusive. There’s still much the scientific community doesn’t know about COVID-19 and the virus that causes it (SARS-CoV-2).

What’s become clear over the past year, since SARS-CoV-2 emerged, is that COVID reinfection occurs but is rare. Here’s what is known so far about COVID reinfection after recovery.

How COVID-19 Reinfection Works

Usually, when you get sick from a virus, your body produces antibodies specific for proteins that the virus makes. The antibodies recognize and target the virus, stimulating your immune system to swiftly neutralize it should that specific germ ever show up in your body again. This is immunity: Your immune system protects you from becoming ill if you are reinfected. It may also protect you from becoming infected in the first place.

Immunity is not universal, of course; if it were, then we all would be immune to the common cold virus. The fact is, even small variations in how a virus is assembled can make it impossible for our immune system to recognize that specific germ. What’s more, antibodies and immune systems are not all the same strength. Antibodies can lose strength with time; and, some people have poorly functioning immune systems.

In the case of COVID-19, researchers have established that most people infected with SARS-Co-V produce antibodies to it. If you are exposed to SARS-CoV-2 again after recovering from COVID-19, then, theoretically, your immune system will neutralize the virus before you become sick a second time.

However, some people have experienced COVID-19 reinfection after recovery. Researchers are asking why this might be possible, and a couple of hypotheses have emerged. First, perhaps the virus changes enough that the immune system doesn’t recognize it when the body encounters it a second time. (This is what happens with the influenza virus year to year.) Second, perhaps our natural antibodies don’t last long enough to defend against a second infection. However, in a large U.K. study, antibodies remained active for at least six months and reinfection within six months was rare. Another large U.K. study concluded that infection reduced the risk of reinfection by 84%.

To understand how COVID-19 reinfection occurs, researchers first confirm any suspected reinfection cases by analyzing the genetic makeup of the precise virus that caused the second illness. Like most viruses, SARS-CoV-2 comes in various strains. A person is reinfected if the analysis reveals that a different strain of the virus caused the second infection. A person who tests positive for the same strain of the virus is not considered a reinfection, but a lingering initial infection. (Molecular tests have detected viral genetic material in patients up to 12 weeks after recovering from the initial illness.) Although more contagious variants of SARS-CoV-2 are coming out, at least some of them are still recognized by antibodies. It is too early to know if reinfection is more likely with the identified variants.

Are COVID Reinfections Worse Than the First Illness?

Genetic analysis has confirmed a few dozen reinfection cases worldwide. Most are milder than the first illness, but one reinfection case involving a 25-year-old man was worse than his first case of COVID-19. This finding puzzles researchers. They expected the reinfection to produce milder symptoms than the initial illness, as the immune system at least partially fights off the second infection. A second person, in Ecuador, likewise experienced more severe symptoms upon reinfection.

As researchers continue to investigate COVID reinfection, they will be closely monitoring how symptoms progress in those known to have become sick a second time.

What Does the Possibility of COVID Reinfection Mean for Most People?

It’s important to stress that COVID reinfection seems to be extremely rare. Of tens of millions of cases of COVID-19 globally, less than a few dozen cases of reinfection have been identified so far. Most people don’t need to worry about reinfection after recovery from COVID-19. Exceptions may be people who are immunocompromised.

However, researchers are keenly watching the reinfection picture because it might offer clues to how the immune system responds to SARS-CoV-2. The reinfection data may yield insight into questions like:

  • Does the body produce antibodies that protect against COVID reinfection? Antibodies do seem to be protective, but antibody strength likely varies from person to person and may vary by severity of disease.
  • How long do these natural antibodies last? Some studies indicate antibodies against the virus last up to six months, possibly longer, but this may also vary between people.
  • Exactly which cells, proteins and other substances contribute to producing immunity from SARS-CoV-2?

The answer to these questions may not only help researchers keep people safe from COVID reinfection but may influence how COVID-19 vaccine development in the future. For the moment, the best thing to remember is the chance of getting COVID a second time after recovery is low. If you develop new COVID-like symptoms after you’ve already had the illness once, be sure to report these new symptoms to your doctor as soon as possible. Most COVID-19 symptoms overlap with other infections, such as the common cold, and that may be the cause of your symptoms.

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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2020 Dec 1
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