If you have also been vaccinated with the booster dose Covid-19 you probably won't need another for months, or even years, recent studies suggest.
The Omicron variant is capable of escaping neutralizing antibodies that provide two doses of vaccine. But the booster dose of mRNA vaccines prompts the immune system to produce a wider range of antibodies, from which any new variant would be difficult to escape, according to the latest study, which has not yet been independently tested and is being pre-published. .
"We are beginning to see a decline in benefit as the number of additional doses increases," John Were, director of the Institute of Immunology at the University of Pennsylvania, told the New York Times. A fourth dose may be necessary in people over 3 or other groups, but for most it seems unnecessary, he said.
Cellular immunity
But antibodies are only one side of immunity. The T and B cells of the so-called cellular immunity also play an important role, recognizing more points of the virus's protein-'s than antibodies, but they are much more difficult to measure.
In the case of SARS, which killed about 800 people in the 2003 Asian epidemic, T-cell-recognizing T cells survive for at least 17 years, according to a 2020 study published in Nature.
From left, human red blood cell, theocyte and T lymphocyte (NCI-Frederick)
In the case of SARS-CoV-2, three studies published in leading science last month show that T cells produced after vaccination (with Pfizer, Moderna, Joghnson & Jonhnson or Novavax vaccines) retain 80 % of their effectiveness against the Omicron variant. Since Omicron carries numerous mutations, it is likely that T cells will remain effective in future variants.
"Memory reactions can take a long time," Wendy Bergers, a Cape Tanun University immunologist and head of one of the studies, told the New York Times.
"I would say T cells are probably more important than most people think," said Dan Maruk of Beth Israel Medical Center in Boston, who led a second study in Nature. Two more studies of similar findings are published in Nature Medicine and in the also reputable Cell.
B cells
Other research looks at the role of B cells, which continue to remember the virus and can produce new antibodies within five days of re-exposure to the virus.
In combination, the protective effect of T and B cells may explain why people affected by Covid-19 although they had received a booster dose it is unlikely that they would become seriously ill.
A new study in Nature shows that, six months after the initial vaccination, B cells continue to mature and produce increasingly effective antibodies, which can recognize a wider range of mutations. Research even shows that the third vaccine produces a wider range of B cells, which retain most of their effectiveness against the Beta, Delta and Omicron variants.
So it seems that in most people the immunity to the coronavirus is maintained for a long time and can cope with the new variants. Even if some areas of the virus mutate, there will always be other areas recognized by T and B cells.
But there are exceptions. According to the study in Nature Medicine, one in five vaccinated individuals showed a significant reduction in the levels of protection that T cells offer against Omicron. The cause of the fall remains unknown, but it is most likely related to the genetic profile, the researchers said.
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