Confirmed! The human immune system can "remember" the new coronavirus for more than a year

After fighting off the attack of the new coronavirus, can our immune system "remember"?

If so, does one have the chance to be immune to COVID-19 once? If not, how long should it take to strengthen immunity?

The issue of human immune memory after COVID-19 infection has always been the focus of responding to the epidemic. On October 5, Liu Jun, a researcher at the Institute of Viral Diseases of the Chinese Center for Disease Control and Prevention, and a team of academicians Gao Fu and Wu Guizhen published a study in the authoritative journal Clinical Infectious Diseases showing that the human immune memory to COVID-19 can last for more than one year, and the proportion of recovered patients who still have COVID-19-specific neutralizing antibodies and T cell immune memory one year after infection is 95% and 92%, respectively.

"We conducted follow-up visits to 101 recovered COVID-19 patients six months and one year later, and conducted multiple tests on serum samples, including neutralization reactions to live viruses and virus-specific detection of immune memory T cells, to detect whether immune antibodies and immune memory T cells still existed." On October 7, Liu Jun, one of the corresponding authors of the paper and a researcher at the Institute of Viral Disease Prevention and Control, Chinese Center for Disease Control and Prevention, told Science and Technology Daily.

“Chasing” immune memory

How to trace immune memory?

If you want to know whether a person has memory, just ask: Do you remember?

"If we want to know whether the immune system has memory of the new coronavirus infection, we need to find out whether there are related T cells and B cells." Liu Jun introduced that acquired immune factors such as T cells and B cells are the key to immune memory.

Flow chart of the follow-up study on immune memory of recovered COVID-19 patients

Therefore, in order to "fish out" cells related to immune memory, research work must first create special "memory fragments" that can match the memory cells related to the new coronavirus as "bait."

This "memory fragment" is the "small fragment" polypeptide of the new coronavirus protein. They will cause "memory flashback" of T cells in the blood cells of people who have recovered from COVID-19, stimulate the immune response again, and finally be discovered through a color reaction.

Therefore, the design of the "bait" is crucial, and it must be both specific and sensitive.

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Targeting the S protein, M protein and N protein on the new coronavirus particles, the team designed specific peptide pools for S1, S2, M and N proteins respectively to "hunt" immune memory cells.

In order to improve specificity, the research team also specially synthesized a tetrameric complex targeting the new coronavirus-specific peptide to conduct a "three-dimensional" search for immune memory T cells.

Within a year, there is no sign of immune memory "fading"

After conducting a comprehensive, three-dimensional search for memory cells in the blood cells of 101 recovered patients, the research team found that 93% of the recovered patients had coronavirus-specific T cell immune memory six months after onset of the disease, and this specific T cell immune memory could last up to 12 months after onset of the disease in 92% of the recovered patients.

"We found that the percentage of virus-specific memory T cells in recovered patients did not decrease significantly 12 months after onset compared with 6 months after onset." Liu Jun said this means that immune memory will continue.

There are different types of immune memory cells. The team also classified and searched for central memory T cells and effector memory T cells, and the results showed that the latter accounted for the majority.

"This means that virus-specific T cell immune memory still exists and can be used to resist reinfection," said Liu Jun.

What’s even more interesting is that the level of T cell immune response is positively correlated with the severity of the disease. In other words, the more severe the symptoms of the recovered person during the infection, the “deeper” the immune memory.

At the same time, the level of T cell memory against the S protein is positively correlated with the level of specific antibodies against the new coronavirus, that is, the higher the antibody level, the more significant the T cell immune memory. This shows that the two memory "defense lines" of the human body against the new coronavirus complement each other.

One year later, specific antibodies persisted

The researchers also tested specific antibodies and conducted regular analysis.

Studies have shown that in more than 95% of recovered patients, specific IgG antibodies and neutralizing antibodies can persist for 6 to 12 months after onset, and their titers are positively correlated with the severity of the acute phase. There is no obvious sign of neutralizing antibodies disappearing 6 and 12 months after onset.

Schematic diagram of statistical analysis of antibody and T cell immunity levels in recovered COVID-19 patients

"Specific T cell immune memory and antibodies can last for at least one year, which plays a very positive role in preventing individuals from being infected with the new coronavirus again." Liu Jun said that the research on the characteristics of immune memory and the improvement of related mechanisms will also provide a theoretical basis for the formulation of vaccine strategies.

"We also found that at least 26% of the recovered patients still had detectable IgM antibodies 12 months after the onset of the disease. We speculate that the long-term persistence of IgM in some recovered patients may be one of the infectious immune characteristics of COVID-19, and its mechanism needs further study," said Liu Jun.

It is reported that the research was funded by major scientific and technological projects of the Ministry of Science and Technology and the National Natural Science Foundation (Excellent Young Scientists Fund and Innovative Research Group Project).

Paper link:

https://academic.oup.com/cid/advance-article/doi/10.1093/cid/ciab884/6381561

Source: Science and Technology Daily. The pictures in this article are provided by the interviewees.

Editor: Liu Yiyang

Reviewer: Wang Xiaolong

Final review: Liu Haiying

◎ Science and Technology Daily reporter Zhang Jiaxing