Popularization of research advances on COVID-19

What type of immunity is the most effective?

Acquiring effective immunity is a key element in our fight against the virus. Good immunity gives robust and durable protection. However, there are two types of adaptive immunity against SARS-CoV-2: the first is natural immunity, acquired when infection with the virus takes place, and the other is vaccinal immunity. Their effect may even be cumulative. But how do they combine ? What type of immunity has been acquired by individuals infected by SARS-CoV-2, then vaccinated? Is this immunity more effective against variants?

Adaptive immunity that protects us against pathogens comprises 3 elements: the B lymphocytes, which manufacture antibodies, the CD4+ T lymphocytes, which enable immune activation, and the CD8+ T cells, which kill infected cells. Immune memory, the basis of our protection against COVID-19, which is carried within the different types of lymphocytes, gives long-term protection by keeping the different types of anti-SARS-CoV-2 cells active.

Immunity can be acquired by natural and by vaccinal means. Natural immunity against SARS-CoV-2 has been shown in studies to be very effective, lasting for up to 8 months after infection. Against variants, protection is less clear, but is reduced overall. With vaccinal immunity, protection differs according to the vaccine. Several studies have shown that effectiveness increases in cases of hybrid immunity (natural + vaccinal immunity), especially against variants. Against the South African variant, for example, hybrid immunity is 100 times more effective than natural immunity, and 25 times more effective than vaccinal immunity.

It appears therefore that there is a synergic effect in the case of vaccination of an individual who has been infected by SARS-CoV-2, enabling better protection in these people, notably against emerging variants. For people who have not been infected, a combination of 2 different vaccines for the 1st and 2nd doses (AstraZeneca with Pfizer or Moderna) will also heighten the immune response. All these research discoveries may allow better immunity to be generated against not only COVID-19, but also against other infectious diseases.

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