COVID-19 ‘immune memory’ could last at least 6 months, study suggests

A recently released study suggests that some people may generate a level of COVID-19 “immune memory” that could offer some protection from the coronavirus after infection, and it might last longer than previously believed.

The purpose of the study was to analyze whether people’s bodies can remember the coronavirus and how that can connect to protection from the virus.

According to the study, published in BioRxiv — an online preprint server for biology — immunity to the coronavirus infection that causes COVID-19 may last for at least six months, and potentially much longer, after a person was initially infected.

“Your immune system tends to remember things that were more threatening,” Dr. Shane Crotty, an immune and vaccine scientist and senior co-author of the study, said. “Over 90 percent of people had substantial immune memory.”

The study was comprised of 185 adults in the United States, ages 19 to 81, who had recovered from the coronavirus.

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Observations by researchers showed that individuals may have a significant amount of “immune memory” of the COVID-19 virus, even after six to eight months.

“Most people are making immune memory for at least six-plus months and it looks like a type of immune memory that probably is capable of keeping most people from getting serious disease again,” Crotty said.

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The U.S. Centers for Disease Control and Prevention said that cases of reinfection with COVID-19 have been reported.

The United States had its first reported reinfection of COVID-19 on Oct. 12.

According to a paper published in the medical journal Lancet Infectious Diseases, a Nevada resident originally tested positive for the virus in April and had symptoms including sore throat, cough, headache and nausea. He recovered and tested negative for the virus in May. In early June, he tested positive again for the virus and went to the hospital. He later recovered.

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Scientists and experts have also compared the coronavirus to the flu in its ability to mutate, which further leads to uncertainty in whether long-lasting immunity could really occur if the virus is constantly changing.

But Crotty explained that the immune system recognizes many parts of the virus, meaning that even if the virus mutates in one part, the immune system will still recognize other parts of it.

Still, the findings are in contrast to other studies previously done by researchers that indicate that any immunity to the coronavirus post-infection could wane after just a couple of months.

According to a study from Imperial College London, results of finger-prick tests carried out between June 20 and Sept. 28 found a reduction in the number of people testing positive for COVID-19 antibodies, dropping from 6% to 4.4% in just over three months.

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Another study published on July 11 by researchers at King’s College London found that antibodies detected in the human body which fight the coronavirus declined after just a few weeks, leaving the possibility of widespread “herd immunity” to the virus out of the question.

The researchers found that 60% of the participants built up a “potent” antibody response, while only 17% retained that potency at the end of the three-month study period.

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Meanwhile, another nationwide population-based study published by researchers in Spain in the medical journal “The Lancet” found that despite the high impact of COVID-19 on the country, antibody “prevalence estimates remain low and are clearly insufficient to provide herd immunity."

Crotty said his study aimed to take a different view of the immune system, saying that “those other studies looked at just one piece of the immune system, which was antibodies.”

In Crotty’s study, blood samples were taken and multiple components in the immune system were researched in the adults over time, including antibodies, B cells and T cells.

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“Most people have memory consisting of all three of those parts, so that’s a really good sign,” Crotty said. “The fact that your immune system is recognizing and remembers this virus in multiple ways means that you have multiple different opportunities for your immune system to help protect you some against this virus.”

While the study showed significant immune memory in adults, Crotty said 3-10% of individuals had little immune memory, suggesting that some individuals will be more susceptible to re-infection faster. Researchers could not determine why specific people were different.