Can you get COVID19 if you already had it?

Question: Is it possible for a person to become sick with COVID-19 again after recovering?

Answer: One of the most crucial hurdles for immunologists trying to develop a COVID-19 vaccine is the question of whether people infected with the virus become immune and, if they do, how long that resistance lasts.

For most viruses, immunity is the payoff for getting sick, so the trick in concocting an effective vaccine is to duplicate that immune response. The problem is that, although most infectious disease experts believe COVID-19 patients will develop immunity, they don’t know for sure.

“Certainly for many viruses, we don’t think people get reinfected,” said Art Reingold, professor of epidemiology at the School of Public Health at UC Berkeley. “They get immunity and they are pretty much immune for life. If I was going to bet my 50 cents, I would think once you are infected with this coronavirus you would not be able to be infected again.”

But Reingold and other experts aren’t satisfied with educated bets, especially considering how different viruses display different characteristics when they encounter the human immune response. People who contract measles do develop lifelong immunity, he said, but there is evidence with other diseases — mumps, for instance

— that immunity may wear off over time.

The influenza virus is a good example, Reingold said. People can get the flu every year, he said, because it is a virus that mutates often, creating an infinite number of variations that can each cause a person to get sick.

“It may not be the same virus on a molecular level, but it is still an influenza virus,” he said.

The key to an immune response, Reingold said, is the development of neutralizing antibodies.

But coronaviruses can be unpredictable in how they impact the human immune system. Studies of four seasonal coronaviruses that cause the common cold show that people develop antibodies, but the levels appear to decline slowly over time and people eventually become susceptible again.

The immune response may be stronger for respiratory viruses, like COVID-19. People sickened by SARS, a dangerous coronavirus detected in China in 2002, developed immune responses that have lasted.

The best-known immunity study involving COVID-19 was published in March by scientists in China who infected two rhesus macaques with the virus, causing them mild illness. They were not able to reinfect the monkeys after they recovered.