For Young People, Having COVID-19 Doesn't Fully Protect Against Reinfection

While a previous COVID-19 infection may help ward off an infection in the future, a new study finds that it doesn't offer full protection for everyone.

The April study, which was published in The Lancet Respiratory Medicine, analyzed data from more than 3,000 healthy members of the U.S. Marines Corps, the majority of whom were between the ages of 18 and 20. The study was conducted between May and November 2020.

Researchers found that around 10% of those who were previously infected with SARS-CoV-2, the virus that causes COVID-19, became re-infected with the virus. In comparison, 48% of study participants who had not been previously infected, developed new infections.

The research confirms that “young people who were previously infected can be infected again,” study co-author Stuart Sealfon, MD, a professor of neurobiology and pharmacological science at the Icahn School of Medicine at Mount Sinai in New York, tells Verywell. The findings also show that people “may not be aware” that they’re reinfected, Sealfon says, and “can potentially spread the infection to others.” 

COVID-19 Reinfection

For the study, the recruits went through several stages of testing over many weeks. They received antibody tests when they arrived at their Marine-supervised quarantine facility to establish whether they had previously been infected with COVID-19 and were also tested for a new SARS-CoV-2 infection at the beginning of the quarantine period, followed by tests at weeks one and two of the quarantine.

After quarantine, those who did not have COVID-19 entered basic training and were tested for COVID-19 every two weeks, for six weeks. Those who tested positive during the study period were isolated and given additional testing, including antibody tests.

A total of 2,436 Marines were followed long enough to analyze the reinfection rate. Of those, 189 tested positive for COVID-19 antibodies and 2,247 tested negative for the antibodies. Overall, there were 1,098 new infections during the study, with 19 recruits testing positive for a second infection and 1,079 becoming infected for the first time.

The researchers analyzed the data and found that, in those recruits that had COVID-19 antibodies, those who became reinfected had lower antibody levels than those who did not become reinfected. It's also worth noting that most of the recruits who already had the virus had no symptoms (84%) compared with 68% of asymptomatic cases in those who were infected for the first time.

Previous COVID-19 infection does seem to offer some level of protection, though. Recruits who had COVID-19 in the past had about a fifth of the risk of being infected again compared to those who had never had the virus. 

Experts Stress the Importance of Vaccination

Sealfon says his work suggests that “the cells that remember the way to respond to the infection by COVID can decrease or even disappear over time.”

Each person’s antibody response to a COVID-19 infection can also “be variable,” Richard Watkins, MD, an infectious disease specialist and a professor of internal medicine at the Northeast Ohio Medical University, tells Verywell. “Getting a natural COVID-19 infection might not produce enough antibodies to protect from re-infection."

Because of this, the Centers for Disease Control and Prevention (CDC) recommends that people with a previous COVID-19 infection get vaccinated against the virus.

The study's findings reinforce these recommendations, Sealfon says. “Vaccine presents to the immune system a protein from COVID so that the immune system can learn to respond to it, but it does not have the virus components that can decrease the immune response during a real infection,” he says. “So vaccination has the potential to be more effective than natural infection in preventing future infection.”

The vaccines also “produce a strong antibody response,” particularly the vaccines that use mRNA technology, Watkins adds.

Overall, Sealfon stresses that “it is important to get vaccinated even if you have been previously infected.”

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.