Can you be infected by COVID-19 twice?

New Delhi, Nov 20: Coronavirus is absolutely a new infection in people and people don't have immunity to the virus when the pandemic started. Knowing what immunity to the virus looks like, and how long it lasts, is important for understanding what happens next.

It is known as the innate immune response and includes the release of chemicals that cause inflammation and white blood cells that can destroy infected cells.

How do you become immune to coronavirus?

Our body system is not specific to coronavirus. It will not learn and it will not give us immunity to the coronavirus.

Instead people need the adaptive immune response. This includes cells that produce targeted antibodies that can stick to the virus in order to stop it - and T cells that can attack just the cells infected with the virus, called the cellular response.

But this takes time while studies suggest it takes about 10 days to start making antibodies that can target the coronavirus and the sickest patients develop the strongest immune response.

If the adaptive immune response is powerful enough, it could leave a lasting memory of the infection that will give protection in the future.

Scientists are developing understanding of the role of T-cells but a recent study found people testing negative for coronavirus antibodies may still have some immunity.

How long does immunity last?

Four produce the symptoms of the common cold and immunity is short-lived. Studies showed some patients could be re-infected within a year.

Research at King's College London suggested levels of antibodies that kill coronavirus waned over the three month study.

But even if antibodies disappear, then the cells that manufacture them, called B cells, may still be around. B cells for Spanish Flu have been found in people 90 years after that pandemic.

If the same is true with Covid, then a second infection would be milder than the first.