Which people are more protected, those who have passed Covid naturally or those who have been vaccinated?

The scientific studies published to date suggest that the immunity offered by vaccines could be more durable.

Stock image of vaccination.

In a few months we have managed to exceed 30% of the vaccinated population in Spain. And that invites you to reflect on how is the immunity that we acquire. Is the natural immunity conferred by being infected equivalent to that provided by vaccines against Covid-19? Can we measure that immunity with rapid tests?

To begin with, it must be taken into account that natural immunity after infection is conditioned by the different tactics with which the SARS-Cov-2 virus tries to avoid the immune system. What’s more, the virus is capable of mutating and generate variants that can also be more transmissible and virulent, which also affects the immunity it generates.

It should be noted that both skills are different. That the virus reaches greater transmission implies that could easily spread to a larger number of people, as is currently the case with the delta variant, a candidate to become the dominant variant in a short time. However, a mutation that generates greater virulence would increase the severity even with a very small infection, something that fortunately has not happened so far with SARS-CoV-2.

How immunity is measured

In principle, the natural immunity could be hypothesized as broader because it involves an immune response against a higher number of antigens than the immune response to a single-antigen vaccine. This is the case with many of the current vaccines against Covid-19. Some use the complete protein S (AstraZeneca or Jannsen) as an antigen, and others only the virus entry receptor binding region, called RBD (Pfizer or Moderna).

But a caveat must also be made here, because there is the possibility of creating vaccines against the inactivated virus, as they have done for the SinoVac vaccine. In that case, the immune response that it would induce would be against all the proteins of the virus.

What seems indisputable is that it is not easy to measure the immune response. The antibody response, known as humoral immunity, is examined with rapid serological tests. In contrast, the T cell response or cellular immunity cannot be evaluated with any rapid test.

Finally, if we intend to compare natural immunity and that conferred by vaccines, we must bear in mind that when we vaccinate we seek an immune response that neutralizes the virus and also offers us very long-term protection.

What the data says

Having said all this, the data we have so far tells us that people who have been infected generate a immune response against protein S, which is quite inferior that the immune response generated by vaccines, both RNA (Modern and Pfizer) such as adenovirus (AstraZeneca or Janssen).

On the other hand, it is true that the natural immunity of patients who have suffered from COVID-19 induces a large number of antibodies that they might even last a lifetime. However, infection by the virus does not generate a greater number of neutralizing antibodies than RNA vaccines, for example. Rather it is the other way around: the antibodies that are produced after immunization with RNA vaccines recognize the enemy better than those induced by natural infection. And the same goes for adenovirus vaccines.

The nuance “neutralizing” when talking about antibodies is important, because it evaluates the ability of these antibodies to block the virus. This analysis of its function offers more information on protection than serological tests, which only examine amount of antibodies against the virus.

Regarding the problem of variants, RNA, adenovirus and recombinant protein vaccines with a vaccination schedule of two doses generated enough antibodies neutralizing against beta, alpha and gamma variants. Regarding the delta variant, there are still no clinical studies.

Conclusion: getting vaccinated is essential

Ultimately, all studies show that the immunity of the vaccinated induces more protection than natural immunity. Getting vaccinated is essential, even if we have already passed COVID-19.

Another indisputable conclusion is that many more studies of neutralizing antibodies with all available vaccines are worth doing. On the one hand, to compare between them and with the neutralizing antibodies of COVID-19 patients, whether they are asymptomatic, mild or severe. But also to carry out epidemiological studies that evaluate the importance of vaccines in the pandemic.

*This article was published on The Conversation.

**Carmen Álvarez is a research professor in Sanitary Processes at the Faculty of Education and Faculty of Health Sciences, UNIR.

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