Vaccinations are the best option to help develop immunity against the coronavirus. In addition, the hope is that people who've been exposed to COVID-19 also develop an immunity to it. When you have immunity, your body can recognize and fight off the virus.
People who've had COVID-19 can get sick again and infect other people.
The Omicron variant is more likely to reinfect someone than the previous dominant COVID strain, the Delta variant. You can get reinfected with COVID in 3 months or less. Reinfections are becoming more and more common as immunity wears off and new variants emerge.
How Do We Become Immune?
When germs enter your body, your immune system springs into action. Here's how it works:
- Bacteria and viruses like the one that causes COVID-19 have proteins called antigens on their surfaces. Each type of germ has its own unique antigen.
- White blood cells of your immune system make proteins called antibodies to fight the antigen. Antibodies attach to antigens the way a key fits into a lock, and they destroy the invading germ.
- Once you've been exposed to a virus, your body makes memory cells. If you're exposed to that same virus again, these cells recognize it. They tell your immune system to make antibodies against it.
Vaccines work in much the same way. They expose your body to an antigen that trains your immune system to fight that germ in the future. Because vaccines contain weakened or killed versions of viruses, you become immune without getting sick.
If You've Had COVID-19, Are You Immune?
COVID-19 affects different people in different ways. In addition, there are different strains. Health experts don't know how long immunity to COVID-19 will last after we're infected. Some reinfections involve the same strains.
Previously known types of coronaviruses appear to trigger some immunity. Studies show that people are protected against the coronaviruses that cause the common cold for up to a year after an infection. And our bodies have antibodies against the virus that causes severe acute respiratory syndrome (SARS) for up to 4 years.
Most people who've recovered from COVID-19 have antibodies against the virus. But there's no evidence that this will protect them if they're exposed to it again or come in contact with a new strain of the virus.
Early on, some researchers thought the antibodies in convalescent plasma (the liquid part of blood) from people who’ve recovered from COVID-19 might help people who are sick with the disease. But the World Health Organization now advises against it. Researchers say convalescent plasma doesn’t improve survival or lessen the need for a ventilator.
Could Herd Immunity Protect Us?
Herd immunity happens when a large part of the population -- the herd -- is immune to a virus. This can happen either because these people got vaccinated or had already been infected. Herd immunity makes it harder for a virus to spread. So even those who haven't been sick or vaccinated have some protection.
Early in the pandemic, it was hoped that herd immunity might be possible, but the rate at which the virus spread and mutated eventually made it apparent that it wouldn’t happen.
How Do We Test for Immunity?
Antibody tests, also called serology tests, measure antibodies to coronavirus in the blood. If you have antibodies, it means you've been vaccinated or exposed to the virus and your immune system has made antibodies against it. Antibody tests are different from the tests doctors use to check for the virus itself.
Testing for antibodies too soon after an illness can also cause false results. It takes 5-10 days after you get infected to develop antibodies against the SARS-CoV-2 virus.