How Protective are COVID-19 Vaccines in Long Term? Do We Require Booster Dose?

A small study suggests that mRNA vaccines such as Pfizer-BioNtech and Moderna COVID-19 vaccines may offer long-term protection for years as long as the virus doesn’t evolve significantly.

Some vaccines for other viruses, such as the MMR vaccine for measles, mumps, and rubella, confer lifelong protection. Other vaccines like influenza may provide only fleeting protection and need to be renewed every year.

Although mRNA vaccines have greatly exceeded experts’ expectations and have shown high efficacy against SARS-CoV-2 and its variants, it is unclear how long this protection can last.

A group of researchers conducted a study to test how long the efficacy of the vaccine can last. This study recruited 41 participants who received two doses of the Pfizer-BioNTech vaccine; out of those 8 had previously been infected with SARS-CoV-2.

The blood samples were collected at the start of the study and then 3, 4, 5, 7, and 15 weeks after the participants received their first dose of the vaccine. It was observed that mRNA vaccine induced robust antibody responses, and the responses were even more potent in people who had recovered from a mild SARS-CoV-2 infection before being vaccinated. Lymph node samples were also collected across this same time span from the 14 participants who were not infected with SARS-CoV-2. The “germinal centers” are the fleeting molecular structures that form inside the lymph nodes in response to infections and vaccinations. In people infected with SARS-CoV-2, these structures include in the lymph nodes of the lungs, which are difficult to access. In contrast, vaccines typically spur their production in the armpits, which is more easily accessible.

The structures train the B cells over weeks and months to bind better to the SARS-CoV-2 virus. The process creates highly trained immune cells, some of which are memory cells that will remember the virus in the long term.

Researchers are unsure how long these “boot camps” last inside the lymph nodes in humans.

But surprisingly, in most of the participants who received the vaccine, their germinal centers continued to be active, training these robust immune cells for at least 15 weeks after the first dose.

As the germinal-center response lasted for months, it likely produced many memory cells that will last for years, and some of these memory cells will likely establish themselves inside the bone marrow and produce lifelong antibodies, said the authors. However, the need for booster shots will depend on the evolution of the virus. Whether the cells produced by the germinal centers are robust enough to handle significantly different variants, they added.

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