Can we be reinfected with COVID-19 after recovery?

A key question in the COVID-19 pandemic has been whether we can be re-infected with the virus after recovering.

There are two scenarios for why someone can test positive twice for COVID-19. The first is that they have genuinely been re-exposed to COVID-19 and that they have caught it again. This can be determined by genetically sequencing the virus during the first and the second test and comparing the viral sequences.

The virus accumulates enough small changes with time that we can distinguish a virus that was caught in July to a virus that was caught now (in October) . The alternative is that the person who caught COVID in July never truly cleared that original infection, in which case this wouldn’t be a ‘new’ case of COVID-19.

Actual re-infection that has been confirmed with genetic sequencing has now been reported in a few rare cases worldwide, indicating that it is indeed possible. 

A study published recently from Hong Kong showed definitively that a 33-year-old man was re-infected.

They established this by sequencing the virus isolated from his first positive test, and comparing that viral genetic sequence to his second positive test (approx. 4.5 months later).

Importantly, during the second infection, the man showed no symptoms. This is how we expect immunity to work: even if we can get re-infected, our immune system is able to respond quickly enough because of its existing antibodies and T cells so that we don’t get sick.

Even though the man showed no symptoms, he was still infectious – meaning he could still transmit the virus, which means that herd immunity through natural infection may not be the best approach.

For the sake of accurate tracking of COVID-19 transmission, it is important for them to determine if a follow-up positive result is indeed re-infection or a persistent original infection. It is important to note that after you clear an infection you are not necessarily protected from re-infection if your are re-exposed to the virus--but we anticipate that you would be protected from developing severe disease.

Vaccines are designed to mimic that first natural infection, but we expect and hope that they will protect us from getting symptoms AND from transmitting the virus.

More widespread studies are needed to establish how common this re-infection is and how it affects people of different age groups and risk factors.

Last updated:
1 June 2021