A study has shown that a combination of natural infection with a single dose of vaccine provides greater immunity than either natural infection without vaccination or full vaccination in individuals.

What is the new study?

• People without prior infection but fully vaccinated with the Pfizer or AstraZeneca vaccine showed a decline in neutralising antibodies over a period of three to seven months.
• But the decline was much less in vaccinated people with prior infection.
• People with hybrid immunity had a higher and more durable neutralising antibody response.
• The hybrid immunity offers stronger protection than just infection or full vaccination alone.

What is Hybrid Immunity?

• It is natural immunity from an infection combined with the immunity provided by the vaccine.
• The immunological advantage from hybrid immunity arises mostly from memory B cells.

What are memory B cells?

• In immunology, a memory B cell (MBC) is a type of B lymphocyte that forms part of the adaptive immune system.
• B lymphocytes are the cells of the immune system that make antibodies to invade pathogens like viruses.
• They form memory cells that remember the same pathogen for faster antibody production in future infections.

How do they assist hybrid immunity?

• While the bulk of antibodies after infection or vaccination decline after a short while, the memory B cells get triggered on subsequent infection or vaccination.
• The memory B cells triggered by infection and those triggered by vaccination have different responses to viruses.
• Infection and vaccination expose the spike protein to the immune system in vastly different ways.
• After full vaccination, antibodies produced by natural infection continued to grow in potency and their breadth against variants for a year after infection.
• Unlike after vaccination, the memory B cells formed after natural infection are more likely to make antibodies that block immune-evading variants.

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