Why is the flu vaccine repeated? Scientists find the key reason

Every year, the government and public health organizations advise the public to get the flu vaccine. But so far, the effectiveness of flu vaccines has not been satisfactory, and the protection they provide is often only a short period of time.

In August, a study in "Science" found the key to why it is impossible to say goodbye to the flu: bone marrow plasma cells. After vaccination, the bone marrow plasma cells that become active quickly will be inactivated within a few months. This discovery may provide new ideas for vaccine durability research.

Measles, rubella, and diphtheria vaccines can provide lifelong protection with a single injection, and these vaccines are most effective. But the flu vaccine cannot do this, and its effectiveness changes every year. If you live in a temperate zone, the effectiveness of the vaccine given in early autumn is likely to disappear before the end of the winter that year.

Jalafi Ahmed, an immunologist at Emory University School of Medicine, has long focused on B cells in the bone marrow. B cells can produce antibodies to defend against viruses. In 1996, Ahmed discovered that there are B cells in the bone marrow-bone marrow plasma cells that continuously produce antibodies after vaccination or infection with viruses, and some bone marrow plasma cells can survive for many years. In theory, this means that such cells can provide permanent immunity.

Memory B cells also produce antibodies in the same way, but compared with bone marrow plasma cells, the former are less stable. Moreover, only after being exposed to a specific virus again, memory B cells will speed up their recognition. This means that high levels of antibodies can only be produced several days after being infected with the virus, which is the disadvantage of current influenza vaccines.

Ahmed and others repeatedly checked the bone marrow and blood of 53 vaccine recipients. Volunteers are between 20 and 45 years old, and within a few weeks and months before and after the flu vaccine, their bone marrow and blood will be taken, and the researcher will examine the samples.

The researchers found that four weeks after the flu vaccine, bone marrow plasma cells that are resistant to the flu virus can be observed in the blood, but these cells disappear after one year.

Although this study did not find longer-lasting protective bone marrow plasma cells, it provided other people with research ideas: for example, producing more bone marrow plasma cells, or stimulating bone marrow plasma cells to protect longer.

At present, adding an adjuvant to the vaccine may be the solution, which helps increase the content of viral proteins in the vaccine. Adding adjuvants is very common in vaccines, but it is not clear whether adjuvants can trigger longer-lasting protection of bone marrow plasma cells, and as of now, most influenza vaccines on the market do not contain adjuvants.

"I hope that people will no longer receive adjuvant-free vaccines in the next ten years, but it is still difficult for the entire industry to change." Ahmed said.