How long does immunity against Covid last? Will the second time be worse? How can I prepare?

If you are one of the millions of Americans who have already had Covid, you may be questioning how long you will have immunity to the coronavirus. At the beginning of the pandemic, most people imagined that being infected had at least one advantage: that you would be protected from future encounters with the virus. But with the latest wave moving to the western US and the virus showing no signs of abating, reinfections appear to have become commonplace. Many people already report that they have become infected for a second or even a third time, with newer variants.

Experts warn that exposure to the coronavirus — through vaccination or infection — doesn’t mean you’re completely protected from future infections. Instead, the coronavirus is evolving to behave more like its “cousins” that cause the common cold and infect people multiple times over a lifetime.

“From the beginning of this pandemic I think that Covid-19 will end up becoming an inevitable infection that everyone will contract multiple times, because that’s how a new respiratory virus takes root in the human population,” said Dr. Amesh Adalja, an infectious disease specialist at Johns Hopkins University.

But the coronavirus still doesn’t fit into clear seasonal patterns like the other viruses that cause the common cold. In addition, it can cause debilitating symptoms that persist for months or years in some people, not to mention the death of millions of others. What can you do to protect yourself, not just from infection but from reinfection? We asked this and other questions common to some experts.

How long will my immunity last after I get Covid?

Before the arrival of the omicron, cases of reinfection were rare. A team of scientists led by epidemiologist Laith Abu-Raddad of Weill Cornell Medicine-Qatar estimated that an attack with delta or an earlier strain of the virus was 90% effective in preventing reinfection in vaccinated or unvaccinated people. “But the omicron changed that calculation completely,” he explained.

Since the emergence of the omicron, past infections offer only 50% protection against reinfection, according to the Abu-Raddad study. The coronavirus has acquired so many mutations in its spike protein that newer versions have become more transmissible and better able to bypass immunity. That is to say, you can contract a version of the omicron after recovering from an older, non-omicron variant. It may even fall ill with one of the newer subvariants of the omicron after outgrowing a different version of the variant.

And there are other factors that increase vulnerability to reinfection, starting with how long it’s been since you’ve had Covid. Immune defenses tend to wane after an infection. A study published in October 2021 estimated that reinfection can occur three months after a person contracts Covid. While these findings were based on the coronavirus genome and explained the predicted drop in antibodies that could fight the virus, the study did not take into account new variants, such as the omicron, that are radically different from older variants.

Because the onomicron is so different from older variants, the protection it affords the person who has contracted it can wane in even less time. In a study published in February and not yet peer-reviewed, scientists from Denmark found that some people were reinfected with the BA.2 sub-strain of the omicron just 20 days after being infected with the original omicron, BA.1.

Because the virus is infecting more people now, our chances of being exposed and reinfected are also higher, said Abu-Raddad.

And while it’s unclear whether some people are simply more susceptible to reinfection with Covid-19, researchers are starting to find some clues. Older or immunocompromised people can produce very few or very low quality antibodies, leaving them more vulnerable to reinfection, Abu-Raddad said. And early research shows that a small group of people have a genetic flaw that paralyzes a crucial immune molecule called interferon type I, putting them at greater risk of developing severe Covid symptoms. It is possible that additional studies will find that these differences also play a role in reinfection.

For now, you should view any new symptoms, including fever, sore throat, runny nose, or change in taste or smell, as a potential case of Covid and get tested to confirm you are positive again.

Will subsequent infections be more or less severe?

The good news is that if the virus gets past your initial antibody defenses, your body can summon immune cells, such as T and B lymphocytes, to quash a reinfection. T and B lymphocytes can take a few days to activate and start functioning, but they tend to remember how to fight the virus based on previous encounters.

“Your immune system has all kinds of weapons to try to stop the virus, even if it comes through the front door,” said virologist Shane Crotty of the La Jolla Institute of Immunology in California.

Many of these immune cells build their protections iteratively, Crotty said. Therefore, those who received the vaccine and the booster are especially well equipped to face the coronavirus. Likewise, people who have been infected before are able to prevent the virus from replicating at high levels if they are reinfected. And most people who have already received the vaccine and are also infected gain a hybrid immunity that offers perhaps the best protection.

Thanks to this, the second or third infection will likely be less severe and will last a shorter time.

Abu-Raddad, who tracks reinfections among large groups of people in Qatar, has already begun to see this promising pattern in patient medical records: of the more than 1,300 reinfections his team identified between the start of the pandemic and May 2021, none led to one ICU admission and none resulted in death.

But the fact that reinfections are less severe doesn’t mean they don’t cause suffering. You may still have a fever and experience body aches, confusion, and other symptoms. And there’s no way to know if his symptoms will continue and turn into persistent Covid, Adalja said.

It is possible that each Covid infection forces a person to face Russian roulette, although some researchers assume that the risk is greater shortly after the first infection. One of the risk factors for persistent Covid is having high levels of virus in your system early in an infection, and you’re likely to have a high viral load the first time you’re infected, Abu-Raddad said. In subsequent infections, your body is better prepared to fight the coronavirus, so it may be able to keep the virus at low levels until it is completely eliminated.

What can we do to reduce the risk of reinfection?

Many of the tools and behaviors that help protect against infection can still help prevent reinfection, Abu-Raddad said. “There is no magic solution against Covid reinfection,” he said.

It is recommended to receive the vaccine and booster, for example, even if you have already had Covid. Just wait a few weeks after an infection to get the injection. Vaccines will raise your antibody levels, and research shows they are effective in preventing serious outcomes if you get sick again. “Scientific confidence in vaccine-induced immunity was and is much greater than in infection-induced immunity,” Crotty said.

Additional measures, such as wearing a mask indoors and in crowded places, respecting social distancing, and improving ventilation where possible, can increase protection. But since most people and communities have already put those precautions aside, it’s up to each person to decide when to take extra precautions, based on their risk of contracting Covid and the extent to which they want to avoid it.

“If you had Covid last week, you probably don’t need to wear a mask today,” Adalja said. “But if it’s been a month, and if there are new variants circulating in the country, it might make sense for people at high risk to take care. People who want to avoid getting Covid because they’re going on a cruise soon or because they need a PCR test negative for some other reason would also do well to take precautions. Covid protections don’t have to be the same for everyone.”

^{Translation by Clara Allain}