Is immunity better after a vaccine or after a natural infection?

Does the vaccine provide better immunity than a natural infection? Hard to say. ” Certain diseases such as measles, rubella, varicella or theHepatitis B result in sterilizing immunity, that is, once you have had it you cannot to be infected a second time », Explains virologist Bruno Lina, director of CNR Lyon and member of the Scientific Council. In this case vaccination and infection confer identical immunity. ” On the other hand, with regard to respiratory viruses such as coronavirus at the origin of the common cold or the respiratory syncytial virus (RSV), one is frequently re-infected “. It is even possible to catch a cold four or five times in the same season !

Regarding Covid-19, it seems that immunity is not sterilizing since several cases of reinfection have been reported. But the natural immune response is highly variable among individuals. ” Usually the more severe the form, the stronger the immunity. », Assures Bruno Lina. In asymptomatic patients, on the other hand, the production ofantibody is sometimes very low. Between 2 and 8% of patients wouldn’t even develop antibodies at all. According to another study from the University of Oxford, 26% of symptomatic patients no longer have a significant immune response six months after infection.

What about after vaccination? Even if the immune response is again quite variable (for example the vaccine is less effective in the elderly), it seems to be more protective against re-infections and severe forms. A small pre-published study on the server bioRxiv shows that the antibody level after two doses of the vaccine RNA is up to 10 times that after natural infection.

Why is the immune response different with the vaccine and after infection?

“The truth is, we don’t know! ” recognizes Sabra Klein, immunologist at Johns Hopkins Bloomberg School of Public Health (Marymand, United States). ” You might think that an infection provides a stronger immunity, because it relies on the totality of the antigens of the virus, whereas the vaccines rely only on the antigen of the virus. protein peak. But this is not the case. It is as if the immune system put on blinders and focus on that piece of the virus “. By scattering its antibody production to less useful parts, the natural immune response would be less effective.

It is also possible that this difference can only be explained by the very large doses of advanced proteins administered in the vaccines (up to 100 micrograms of messenger RNA per dose for the Moderna vaccine for example). ” However, since the vaccines are administered through the muscle, they do not offer protection at the level of the muscle. mucous», Emphasizes Bruno Lina. This means that the virus can persist in the nose or throat and that even the person vaccinated has the potential to remain infectious.

Should people who are already infected be vaccinated?

The High Authority of Health advises people who have contracted the virus to be vaccinated with a single dose about 6 months after infection. ” This is even by far the best thing that can happen., confirms Bruno Lina. The infection produces a humoral and mucosal response which are both reactivated by vaccination “. Even when the level of antibodies is no longer detectable in infected people, the vaccine will wake them up. lymphocytes B memories that will remake antibodies ad hoc.

According to a study published in Science, 95% of subjects naturally immunized against SARS-CoV-2 and who received one dose of vaccine developed a T cell response directed against the spike protein, compared to 70% in those who had never been infected with SARS-CoV-2 – and who also received a single dose. The number of B lymphocytes directed against the spike protein is even 63 times higher in the first case.

Do natural immunity and vaccines protect against variants?

One might think that having been infected with the original strain in 2020 does not protect against newer variants like Beta or Delta. ” In fact, the infection does offer fairly effective protection. », Assures Bruno Lina. One way to measure this immune response is to perform an “antibody panorama” present in the patient. ” We can thus see in a patient all the antibodies targeting the different epitopes of the different viruses. », Explains the virologist. A study published in PLOS Biology shows for example that 6 of the 79 epitopes of SARS-CoV-2 bind to epitopes of other coronaviruses, which shows a certain dose cross immunization.

And it is the same for the variants. ” Basically, the more distant the viruses are from each other, the less protective the antibodies are., relates Bruno Lina. We see, for example, that people infected with the Beta variant [sud-africain] are less well protected against Alpha variants [anglais] and Delta [indien]. In contrast, people infected with the original strain appear to be better protected against Delta variants and Beta “.

What about vaccines? According to a pre-published study on MedRxiv, the efficacy of the vaccine AstraZeneca is reduced to 60% after two doses against the Delta variant (against 66% against the Alpha variant). Corn another British study confirms that AstraZeneca remains 92% effective against hospitalizations. Regarding the vaccine Pfizer, efficiency would be reduced to 88% with two doses (against 94% for the Alpha variant). In all cases, the laboratories claim to be able to quickly produce effective vaccines against potential variants that escape the immune response.