How is it possible that the majority of hospitalized for covid-19 are vaccinated people?

Jose Manuel Jimenez Guardeño and Ana María Ortega-Prieto




From now on we will see news with headlines saying that most of those hospitalized for covid-19 are people fully vaccinated with the two doses. This is something that, at first glance, can generate confusion and generate more questions than answers:

Does this mean that vaccines don’t work? Will I be safer if I don’t get vaccinated? Are we facing a adverse effect caused by vaccines as the now famous potentiation of antibody-dependent infection or ADE?

The answer to all these questions is no. Vaccines worked for months, they work now and everything indicates that they will continue to work at least in the near future.

Vaccinated people are going to be more protected than unvaccinated people and there is no evidence of RDW.

In fact, what all this means is that we are vaccinating a lot and that you always have to read beyond the headline. Why do they say that there are more hospitalized vaccinated than unvaccinated?

The first thing we have to keep in mind is that the majority of people hospitalized for covid-19 are people who belong to risk groups, mainly people over 60 years old. In fact, this is the main reason why these groups are precisely the first in receiving the different vaccines.

Government of Spain

Therefore, at the present time we find ourselves with the scenario in which the majority of these people in risk groups are already fully vaccinated.

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Taking this into account, and to explain what happens, we are going to use a simple model with hypothetical numbers to make things easier.

Imagine a country with 36 people belonging to risk groups where 91% of these people have received both doses of the vaccine and 9% have not been vaccinated.

In blue we see vaccinated people, and in red those not vaccinated:


Time passes and we see that in the vaccinated group 5 people have become infected requiring hospitalization and in the unvaccinated group this only occurs in 2 people. We already have the headline: 71% of those hospitalized for covid-19 are vaccinated!


Although what the headline says is true, the information is incomplete and can generate a lot of confusion if they do not know how to interpret the data it offers us. If we look at the numbers with a critical eye and taking into account the proportion of vaccinated and unvaccinated, we will see that the reality is very different.

In this case we see that 15% of the vaccinated people have required hospitalization and this percentage rises dramatically to 66% in unvaccinated people.


If we make the calculations taking into account the number of vaccinated and unvaccinated within the same risk group we will see that the holder is very different. In this case it would be more correct to say that vaccines decrease the probability of hospitalization for covid-19 by 77%.

This really isn’t something that can catch us by surprise. On the contrary, it is to be expected when the majority of the population at risk is vaccinated. You just have to think that if 100% of the population were vaccinated, 100% of the hospitalizations would be of vaccinated people.

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100% of the vaccinated population will never be reached because there are people who for various reasons cannot be vaccinated and others (fortunately a minority) who simply prefer not to.

However, although it will not be 100%, vaccination coverage is expected quite tall (at least in adults). In the following image we can see the percentage of the population completely vaccinated in different countries:

Why are people infected after receiving the vaccine?

This occurs mainly because no vaccine is 100% effective. If millions and millions of vaccines are administered, the expectation is that in some cases the protection is not adequate and the person may develop serious forms of the disease and even die. The interesting thing here is to know that this number would be considerably higher if we did not have vaccines.

In the following image we can see the number of doses of the different vaccines administered in the world. In so far this pandemic, more than 3.5 billion doses have been administered:

Also this is something that has already been described using different models. Here we have the example of a model carried out in the United Kingdom where it is estimated that in summer 70% of hospitalizations and deaths will be people who have received two doses of the vaccine.

Therefore and in summary, it is always important not to simply stay in the headline and read the news and the complete information prior to to make conclusions.

Jose Manuel Jimenez Guardeño. Researcher in the Department of Infectious Diseases, King’s College London. Ana Maria Ortega-Prieto, Postdoctoral research associate,
King’s College London.

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A version of this article was originally published on The

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