Popularization of research advances on COVID-19

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The evolution of immunity after vaccination

Infection by SARS-CoV-2 produces B cell responses that express powerful antibodies against the virus. The B cells evolve for at least a year after infection. During this evolution, the effectiveness of the antibodies produced increases, making them notably more potent against emerging variants. Vaccination is different from natural infection (path of virus administration, nature and persistence of the antigen in the body…). So how do the B cells and therefore the antibodies evolve in the months following vaccination? Researchers at New York Rockefeller University studied their evolution 5 months after the 2nd dose of the vaccine.  

They recruited 32 volunteers between the 20th of January and the 20th of July 2021 who had not been infected but who had received the Moderna or Pfizer-BioNTech vaccine (2 vaccines based on mRNA technology). In those individuals having received two injections, B cells were analysed 1,3 months and 5 months after the 2nd dose. They firstly observed that levels of antibodies effective against SARS-CoV-2 increased between the two injections. Similarly, neutralisation of the virus by these antibodies was 12 times higher 6 weeks after the 2nd injection than after the 1st.. However, after the 2nd injection, antibodies reduce significantly over time: 4,3-fold between 6 weeks and 5 months later. The observation was the same regarding effectiveness of neutralisation, which reduced on average 7-fold, 5 months after the 2nd dose. Then the scientists observed that B cells continued to evolve for at least 5 months after the 2nd injection. So the antibody targets remained identical, but affinity for their targets was higher, making them more potent. 

In conclusion, as with natural infection, vaccination against SARS-CoV-2 produces B cells which evolve over several months and enable the expression of more effective antibodies. A 2nd dose of the vaccination therefore enables a stronger response against SARS-CoV-2, but this is not greater than the protection acquired after one dose of the vaccine following natural infection.

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