Why do some vaccine recipients develop covid-19?

Since the start of the vaccination campaign, severe cases of COVID-19 have been significantly reduced. However, some of those who have received the full vaccine regimen still develop COVID-19. This is not to say that vaccines do not work or are less effective; on the contrary, all current data on vaccines show that they are very effective and also very safe, even against new variants.

Recall that vaccines prepare our immune system to recognize and defend itself against the SARS-CoV-2 virus and prevent the development of COVID-19 disease by generating an immune system response against the S protein, which is a specific and exclusive protein of the virus.

A person is considered fully vaccinated if he/she has received all the doses prescribed for each of the vaccines currently on the market. However, a complete schedule does not eliminate the possibility of infection with the virus, as these vaccines do not prevent infection or complete invasion of the virus.

People with a complete vaccination program will then have a trained immune system that will act very quickly in the presence of the virus. But while this is happening, the virus can multiply and the person would be infected but with no symptoms or very mild symptoms and could infect others. The simple fact that the virus faces almost immediate resistance from the immune system leads us to believe that there will be up to a 50% reduction in its ability to transmit.

This in no way means that the vaccine has failed. The complete and total success of the vaccine is the prevention of COVID-19.

COVID-19 vaccines are safe and effective in preventing COVID-19 disease, especially severe cases, the vaccines are not 100% effective, but although their primary goal is not to prevent infection, they do prevent people from developing severe forms of the disease and dying.


  • Infections are expected to occur in vaccinees. COVID-19 vaccines are effective in preventing most infections. However, (as with other vaccines) they are not 100% effective.
  • Fully vaccinated individuals who become infected are less likely to develop severe disease than unvaccinated individuals who become infected with COVID-19.
  • Even when fully vaccinated people do develop symptoms, they tend to be milder than in unvaccinated people.
  • Vaccines against COVID-19 protect people against infection and severe disease, and significantly reduce the likelihood of hospitalization and death.
  • Vaccination is important to reduce the spread of the virus and prevent the emergence of new variants worldwide.
  • Vaccinated people are much better protected against severe disease and death from COVID-19 than unvaccinated people, including variants such as Delta.
  • Vaccination is the best way to slow the spread of COVID-19 and prevent infection with the Delta variant, among others.
  • Infection in vaccinees occurs when a fully vaccinated person becomes infected with the virus that causes COVID-19. Vaccinated persons who become infected may be contagious.
  • Even if you are fully vaccinated, it is important to remember that prevention is still one of the best ways to avoid spreading the virus.
  • Even if you are fully vaccinated, if you live in an area with substantial or high transmission of COVID-19, you, your family, and your community will be better protected by wearing a face mask in enclosed public places.
  • There are groups of people who cannot be vaccinated, either because they have a medical condition that prevents them from being vaccinated or because of their age. In these cases, it is important to wear a mask, keep a safe distance and wash your hands.
  • If you are pregnant, you can be vaccinated against COVID-19.
  • If you are breast-feeding, you can be vaccinated against COVID-19.