Covid: why it is not the same to get coronavirus with a vaccine than without it

Given the explosion of infections by covid-19 of the sixth wave in Spain, the doubt about whether or not being vaccinated makes a significant difference is logical.

It has been heard a lot that “in the end we are infecting almost all of us”.

And, in part, it is true.

But is it the same to pass the disease having previously been vaccinated than without having done so?

Fortunately, it is not the same.

That current vaccines do not completely eliminate the virus in case of contagion it was already known from the publication of preclinical tests carried out on animals.

It was said, and so it has been, that we became asymptomatic carriers.

From data from clinical trials it was concluded that vaccines protect against serious illness and death with a very high percentage.

And, for a global state of emergency, it was considered enough.

Because, as has been shown later, vaccines have decreased both hospital admissions in ICUs and deathsespecially among the vulnerable population.

Other evidence that shows this is that if confirmed cases increase but hospitalizations and deaths increase to a lesser extent, it will mean that many reported cases are causing less severe forms of disease and fewer deaths.

The vaccinated transmit the virus less

Indeed.

Vaccines are being shown to reduce transmission: the probability of infecting decreases in a vaccinated person whose immune system is primed.

The appearance of the omicron variant, much more contagious, could mask this fact.

But there are several studies that show that vaccinated people are contagious for fewer days than unvaccinated people, since their defenses eliminate the virus sooner.

According to a study carried out with the delta variant and published in the New England Journal of Medicinepeople vaccinated clear the virus from your body in about five dayscompared to seven days for people who are not vaccinated.

As researchers from the University of Oxford show in another, yet unreviewed, study, close contacts of vaccinated people were infected less than those of unvaccinated people.

And among vaccinated people, it was found that people who had received two doses (of any vaccine) transmitted lesssa your contacts than people who only received one dose.

So it seems that in vaccinated people, the viruses are not completely eliminated, but the transmission capacity decreases.

we get sick differently

There is plenty of evidence to show that vaccinated people are much less likely to suffer from severe covid-19, including much less chance of hospitalization and death.

In one of the latest studies, conducted by the US Centers for Disease Control and Prevention (CDC), it was shown that having immunity, either from vaccination or previous infection, protects against hospitalization for covid-19 caused mainly by the alpha and delta variants.

Regarding omicron, it is suggested that although people are more likely to be infected with this variant, because it is more transmissible than previous ones, vaccination continues to provide a high level of protection against severe disease and hospitalization also facing omicron.

Two studies have been conducted in the UK examining the Relationship between the omicron variant, vaccination and the risk of hospitalization.

In both studies, it was found a significant reduction in the risk of hospitalization for omicron cases after three doses of the vaccine, compared with those who were not vaccinated.

doNatural infection protects us of subsequent infections?

If the natural infection of covid-19 protected more lastingly against subsequent infections, we would be seeing a decline in severe cases among the unvaccinated, since they are more likely to pass on the infection.

Actually, the opposite happens. The difference in hospitalizations between unvaccinated and vaccinated is increasing. This is easily seen in the United States, where a large percentage of the population is unvaccinated.

In the figure above, which represents the rate of hospitalizations in people over 65 years of age comparing the vaccinated with the unvaccinated, it can be seen that the distance between the curves widens, when it should decrease as the unvaccinated become infected.

From these data we can deduce that immunity produced by natural infection is not durable and that probably lasts two or three months.

We also know that it occurs in a similar way with the protection granted by vaccines, since the decrease in antibodies has motivated the inoculations of the third dose almost universally (although not all immunity resides in them).

The fact that the virus mutates and generates new variants It probably also influences this decrease in protection and the increase in reinfections.

It is clear that the Vaccines do not prevent infection 100% because the virus manages to multiply.

That is, they do not provide sterilizing immunity.

However, thanks to them, the severity and mortality of the disease and hospitalizations have been reduced.

In addition, to a certain extent, they reduce the degree of virus transmissionas we have seen before.

The prospect of obtaining more complete vaccines, which in addition to protecting us against serious illness, eliminate the virus and prevent contagion, opens up as one of the most optimistic solutions in the future.

Hopefully not too far away.

María Mercedes Jiménez Sarmiento is a scientist at the CSIC. She is a specialist in Systems biochemistry of the bacterial division and a scientific communicator at the Margarita Salas Biological Research Center (CIB-CSIC).

Matilde Cañelles López is a Scientific Researcher in Science, Technology and Society at the Institute of Philosophy (IFS-CSIC).

Nuria Eugenia Campillo is Senior Scientist. Specialist in Medicinal Chemistry at the Margarita Salas Biological Research Center (CIB – CSIC).

His original article was published in The Conversation which you can read here.