New study reveals why flu shots fail to give long-lasting immunity

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Influenza vaccines can boost immunity, but this improvement is only short-lived. American researchers recently found that immunization increases the levels of antibodies against the seasonal flu-causing virus only for a few months, after which these levels plateau due to the loss of bone marrow plasma cells (BMPC). BMPC are the cells responsible for producing influenza-specific antibodies after vaccination.

How flu vaccines are supposed to work

The goal of vaccination is to provide long-lasting immunity against a specific infection. A vaccine is made from a small amount of a weakened pathogen, such as a virus or a bacterium, which is then introduced into the body via injection. This prompts the immune system to respond to it by making antibodies specific to the pathogen.

Because the pathogen is weak to begin with, its introduction is expected to help the body develop immunity without causing any sickness. This process of immunization ensures that the next time the body encounters the same pathogen, its immune response will be swift and even more effective than the first time. The success of most vaccines is due, in part, to pathogen-specific antibody responses.

But according to studies, antibody levels peak in the months following vaccination. They then decline and are maintained at a certain level by non-dividing plasma cells that reside in the bone marrow. These cells, called BMPC, have naturally long lives and produce the majority of immunoglobulin G (IgG) — the most common type of antibody found in circulation — present in the blood of humans.

When a person gets vaccinated, some of his resident BMPC begin producing pathogen-specific antibodies in response to the vaccine. In line with this, several studies have found that the total and pathogen-specific antibody levels of a person correlate closely with the amount of BMPC present in his body.

But recent investigations on the effectiveness of influenza vaccines have reported a rapid decline in protective immunity and antibody levels following vaccination. This observation suggests two possibilities: either flu vaccines fail to induce the desired response from BMPC or the BMPC they elicit fail to become long-lived.

A team led by researchers at the Emory Vaccine Center in Atlanta, Georgia explored these possibilities in a study published last month in the journal Science.