Vindictive lymphocytes
Accurate data on the duration of immunity to COVID-19 have been obtained
Australian scientists have developed a special method for testing immunity by memory cells in the blood of patients who have had COVID-19. The results showed that immunity to the new coronavirus infection persists for at least eight months. The study was published in the journal Science Immunology (Hartley et al., Rapid generation of durable B cell memory to SARS-CoV-2 spike and nucleocapsid proteins in COVID-19 and convalescence).
From the very beginning of the pandemic, scientists around the world have been looking for an answer to the question of how long immunity to COVID-19 persists and how great is the risk of re-infection.
Researchers from Monash University, the Burnet Institute and the Alfred Hospital in Melbourne analyzed blood samples for eight months, which they took from 25 volunteers diagnosed with COVID-19. For each participant, the scientists made a series of "snapshots" of the state of the immune system, starting from the 4th and up to the 242nd day of the disease. Another 36 people without signs of the disease made up the control group.
The results showed that the concentration of free antibodies to SARS-CoV-2 in the blood began to fall within 20 days after the first symptoms appeared. This is consistent with the results of previous studies suggesting that antibody levels decrease rapidly, especially in mild cases of COVID-19.
But the task of the scientists was not to see how long the antibodies themselves persist, but for how long the immune system stores the memory of the encounter with the virus.
Antibodies, according to the figurative expression of the authors, are similar to projectiles with which the immune system attacks the pathogen, and the signal for the production of antibodies is given by white blood cells called memory B cells.
In the case of some pathogens, these cells persist for many years. For example, measles causes an antibody reaction that practically does not decrease throughout life. For other pathogens, after a while, the immune system needs a reminder in the form of booster vaccines.
To test whether the immune system familiar with COVID-19 retains enough memory B cells to cope with the virus if it reappears in a few months, the researchers injected fluorescently labeled pieces of SARS-CoV-2 into the blood samples of the subjects.
The analysis not only revealed a significant reaction to COVID-19 in each of the blood samples, but also allowed scientists to determine which types of memory B cells respond to a specific part of the virus.
The results clearly showed that eight months after infection, a strong immune response is formed in the blood of a person who had previously suffered COVID-19.
The viral proteins used by the authors of the study are considered to be the main targets for targeting the vaccines being developed. Hence, scientists conclude that most vaccines should also provide a good level of immunity for at least eight months. This is good news for those who are concerned that COVID-19 vaccines will not provide the proper protection period needed to control the spread of the virus.
"It was like a black cloud hanging over the potential protection that the COVID-19 vaccine can provide," the press release says. Monash University, the words of the head of the study, immunologist Menno van Zelm (Menno van Zelm). "Our results give hope that once vaccines are developed, they will provide long–term protection."
According to the authors, in order to bring the pandemic under control, it is necessary that 70 percent of the population develop immunity. And now it is known that there is a window of at least eight months for this, scientists say.
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