Filenews 11 March 2022
If you've also been vaccinated with the booster dose against Covid-19 you probably won't need another for months, or even years, the latest studies suggest.
The Omikron variant is capable of escaping the neutralizing antibodies that offer two doses of vaccine. But the booster dose of mRNA vaccines encourages the immune system to produce a greater variety of antibodies, from which it would be difficult to escape any new variant, shows the most recent study, which however has not yet undergone independent testing and is presented as a pre-publication.
"We are starting to see a decline in benefit as the number of additional doses increases," John Wery, 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 65 or other groups, but for most it seems unnecessary, he said.
Cellular immunity
But antibodies are only one side of immunity. An important role is also played by the T and B cells of the so-called cellular immunity, which recognize more signs of the virus spike protein than antibodies, but are much more difficult to measure.
In the case of the SARS coronavirus, which killed about 800 people in the 2003 Asian epidemic, T cells that recognize the virus have survived for at least 17 years, a study published in 2020 in Nature showed.
In the case of SARS-CoV-2, three studies published in leading scientific studies in the last month show that T cells produced after vaccination (with the vaccines of Pfizer, Moderna, Johnson & Johnson or Novavax) retain 80% of their effectiveness against the Omikron variant. Since Omikron carries numerous mutations, it is likely that T cells will remain effective in future variants as well.
"Memory reactions can last very long," Wendy Bergers, an immunologist at the University of Cape Tanun and head of one of the studies, which is published in Nature, told the New York Times.
"I would say that T cells are probably more important than many people think," added Dan Maruk of the Beth Israel Medical Center in Boston, head of a second study at Nature. Two more studies of similar findings are published in Nature Medicine and in the also reputable Cell.
B cells
Other research is looking into the role of B cells, which continue to remember the virus and can produce new antibodies within five days after new contact with the virus.
In combination, the protective effect of T and B cells may explain why people who contract Covid-19 even though they had received a booster dose are unlikely to get seriously ill.
A new study in Nature shows that, six months after 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 larger range of B cells, which retain most of their effectiveness against the Beta, Delta and Omikron variants.
So it seems that in most people the immunity to the coronavirus is maintained for a long time and may be coping 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 experienced a significant reduction in the levels of protection offered by T cells against Omikron. The cause of the drop remains unknown, but it is most likely related to the genetic profile, the researchers said.
