Hybrid immunity is more effective than vaccination alone

The link between a strong neutralising antibody response and protection against infection by the virus has been clearly demonstrated. This is why more than 6 billion doses of the vaccine have been given in an attempt to control the pandemic. But the vaccines have been developed from the spike protein of the original Wuhan strain, while the variants that have subsequently emerged allow the virus to partially evade this immunity. In order to better understand the immune response triggered by vaccination, researchers in Sienna, Italy, compared the neutralising antibody responses in vaccinated individuals with prior infection by SARS-CoV-2 and with no prior infection.

The B lymphocytes and the plasma (the part of the blood that contains antibodies) of 10 individuals were analysed. It is the B lymphocytes that produce antibodies. The 10 people studied had been vaccinated against COVID-19 with the Pfizer-BioNTech vaccine, a vaccine based on mRNA technology. Amongst these individuals, 5 had been infected with SARS-CoV-2 prior to vaccination, and 5 had never been infected.

Hybrid immunity means having been infected by the virus, then vaccinated. The scientists discovered that individuals with hybrid immunity had more B lymphocytes directed against SARS-CoV-2 after vaccination. In addition, their plasma neutralised not only the original virus strain more effectively, but also variants such as Alpha (UK), Beta (South African), Gamma (Brazilian) and Delta (Indian). And the neutralising antibodies were more potent in individuals with prior infection.

Hybrid immunity is therefore more effective against COVID-19 than vaccination on its own. Now it will be necessary to analyse immune responses after the 3^rd dose of the vaccine.