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A new study has provided evidence that immune memory in recovering coronavirus patients is likely to persist for at least eight months, according to Business Insider.
This “memory” is not based only on antibodies: it is also related to white blood cells, called T and B cells, which have impressive “memory” powers.
Together, these two layers of protection allow the immune system to recognize the coronavirus and attack it again if it ever invades again, preventing reinfection.
To assess how long immunity to the virus persists through all these layers of the immune system, the researchers looked at how many and what type of immune cells the COVID-19 patients had after recovery.
Although a new study by scientists has yet to be reviewed, it does give hope that those who have already contracted the coronavirus probably will not contract it for quite some time.
“Most people develop most of the immune response to the virus and the protection of these parts still works for about six to eight months. That sounds like bad news, ”said Shane Crotty, a virologist and co-author at the La Jolla Institute of Immunology in California.
Antibodies disappear, but T and B cells remain
Some studies show that antibodies to coronavirus, the proteins in the blood that protect the body from reinfection, disappear within a few months.
However, this problem can be alleviated by the function of killer T cells, which identify and destroy infected cells, as well as helper T cells that inform B cells about how to make new antibodies.
“All of these elements are designed to work together: if one part of the immune system is not strong in anyone, the other can compensate. Then it would be logical to measure everything, ”says Crotty. His team of researchers measured both types of T cells, as well as B cells and antibodies in blood samples taken from 185 people who recovered from COVID-19.
Nearly 40 participants donated blood multiple times, some more than six months after illness. This allowed the researchers to assess how the patients’ immune responses changed over time.
Their results showed that coronavirus-specific T cells were slightly depleted in 4-6 months and then stabilized. Researchers believe this is because T cells and antibodies remain at this level after 6 months, and this is typical for other viruses as well.
“After infection, antibodies and T-cell responses develop between 1 and 2 weeks after infection. Then they multiply and the amount reaches a peak. In 4-6 months, their numbers are decreasing, but they stabilize at around six, ”says Alessandro Sette, another immunologist at the La Jolla Institute and co-author of S. Crotty.
The study results also showed that B cell levels increased in patients between the first and six months. This is especially good, explains Sette, because B cells are a source of future antibodies.
“When the initial virus invasion wears off, the B cells stop fighting, they stop producing antibodies, but they are still there if the virus attack resumes: if an expanding army of B cells circulates in the body, it regenerates the antibody response “Sette said.
However, antibodies drop markedly in the six-month limit. However, Ms Crotty says such a decrease is “pretty typical of any infection” and does not cause anxiety.
T cells targeting coronavirus can exist for years
Sette and Crotty have only been able to follow patients for eight months since they became infected, as the pandemic began about a year ago. But they believe that the slow decline in the number of T and B cells in patients means that these cells will last much longer than the period analyzed in the study.
“The immune responses are in line with the predicted scenario and are stable for at least eight months,” Sette said, adding that “the trajectory does not indicate that they will fail after eight months and one day.”
White blood cells that develop in response to other viruses can survive for many years. Here, smallpox-specific T cells survive for about 10 years, while B cells, in the case of smallpox, persist for up to 60 years.
Characteristic T cells of SARS, another coronavirus that shares 80% with this new SARS-CoV-2 coronavirus. their genetic code also appears to be durable.
A study in July looked for T cells in blood samples from 23 people who survived SARS. And the survivor, even 17 years after the disease, still had SARS-specific “memory” T cells.
Few patients have a weak immune memory
A study by S. Crotty found that about 90 percent. people develop strong immunity to coronavirus based on antibodies and T and B cells.
But not everyone creates all three immune elements at the same level, and for a small subset of participants, only some or none of the immune elements have developed.
Crotty noted that those patients had “relatively weak immune memory,” so they could become infected with COVID-19 again relatively quickly.
“I really want the whole orchestra of the immune system to come together to fight the virus,” says Sette. The reason for this difference between people is unclear, but the study authors found that various types of immune cells worked in patients who were better able to manage COVID-19. Those who performed worse had one cell type or less.
But until scientists have a chance to study the new coronavirus over a longer period of time, there will be no way to predict how long immunity will last, Sette and Crotty say.
“There is just no way to do a quick blood test to tell you that your immune memory will last 10 years. You’ll have to wait and watch, “says Crotty.
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