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Why don’t seasonal flu shot have long term effect?

A group of researchers from the Emory Vaccine Center provides a view about why the seasonal flu vaccination’s boost in immunity doesn’t last for many years, unlike some childhood vaccinations. Science journal published this article on August 13.

Bone marrow is the home base for immune cells which produce antibodies. Thus, in bone marrow, only the seasonal flu vaccination increases the number of antibody-producing cells. These antibodies are specific for flu in the bone marrow. However, most of the newly generated cells don’t produce antibodies within a year of vaccination, Emory researchers found.

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The reason behind antibody declination in flu vaccination

The researchers are trying to propose a design of longer-lasting “universal” flu vaccines, as well as vaccine studies against SARS-CoV-2. Every year you must take a flu vaccine because the influenza virus that infects humans mutate and swap genes with viruses from birds and pigs. Not only that but also the vaccine decline over time that this highlights.

Researchers conducted vaccine studies.

Most vaccine studies collect blood samples from participants. The antibody-producing cells are present in the blood samples after a few weeks of vaccination. Rafi Ahmed, Ph.D., and the director of Emory Vaccine Center who led the study obtained bone marrow samples which are a more invasive procedure.

Most people have some flu-specific plasma cells – a type of immune cells which secretes antibodies in large amounts. So the researchers decided to distinguish between antibodies produced by pre-existing cells and antibody production after the flu vaccine shot.

Carl Davis, Ph.D., is the first author of this and also a postdoctoral fellow in Ahmed’s laboratory. Davis said that they were able to follow the cells produced by the vaccine because they produced unique antibodies. These antibodies can be identified with the help of sequencing techniques.

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Why is bone marrow so important?

Moreover, they could see the new antibodies produced in the bone marrow due to vaccination contracted after one year. On the other hand, the antibodies present in the bone marrow in response to influenza before the vaccine shot stayed at a constant level over one year.

Ahmed says that just getting to the bone marrow is not enough. Moreover, a plasma cell has to find a niche in the bone marrow and get into it. Furthermore, it should undergo gene expression, and metabolic changes could promote longevity.

From 2009 – 2018, the bone marrow collection was conducted in collaboration with Edmund K. Waller, MD, PhD. He is also a professor of haematology and medical oncology, medicine, and pathology at Emory University School of Medicine and Winship Cancer Institute.

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Flu vaccine study

In this study, 53 participants agreed to give their bone marrow before seasonal flu vaccination. After one month, with follow-ups for a year later. Likewise, vaccination increased the proportion of flu-specific cells after a month. After that, the follow-up months later revealed that antibody count had declined to the baseline.

For finding a new vaccine-specific antibody-secreting cell require analyses of both the cells’ DNA and also examine the antibodies they make. In addition to this tracking, those cells’ abundance in blood and bone marrow is also essential. One of the good news for volunteers in this study is that the levels of antibody-secreting cells in blood correlate with long-term effect in the bone marrow. This antibody-secreting cells could help researchers continue to monitor the immune responses in the volunteers.

Vaccine additives

Furthermore, vaccine additives called adjuvants also increase long-term bone marrow homing for antibody-secreting cells, says Ahmed. Adjuvants promote the formation of germinal centres and structures in the lymph nodes. In lymph nodes only, plasma cells produce high-affinity antibodies. However, these structures are essential for encouraging long-lived plasma cell production.

Get more information from the article, Influenza vaccine-induced human bone marrow plasma cells decline within a year after vaccination.”

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