Countries with the most fully vaccinated people 0:52
(CNN Español) –– More than 5,000 fully vaccinated people in the United States contracted coronavirusaccording to the Centers for Disease Control and Prevention (CDC).
How do you explain this? Dr. Elmer Huerta looks at the CDC data and recalls how vaccines work.
You can listen to this episode on Spotify or your favorite podcast platform or read the transcript below.
Hello, I am Dr. Elmer Huerta and this is your daily dose of information on the new coronavirus. Information that we hope will be useful to take care of your health and that of your family.
Vaccinated people and the coronavirus
A piece of news that went around the world –– arousing various types of reactions–– is the one published on Wednesday on the data that the Centers for Disease Control and Prevention (CDC) shared with CNN.
In an email, the CDC revealed that there had been 5,800 cases of Covid-19 in people who had completed their vaccination in the United States, of which 396 were hospitalized and 74 of them died.
Due to the surprise that it caused in many people that someone who is fully vaccinated can get sick, hospitalize and even die from covid-19, today we will see how this apparently paradoxical phenomenon is explained.
First of all, as we explained in the March 4 episode, it is very important to understand the difference between two concepts that tend to get confused: efficacy and effectiveness of vaccines.
What is the efficacy of a vaccine?
Let us remember that in phase 3 of the clinical stage of vaccine development, thousands of volunteers are invited to participate in a study, in which the vaccine candidate faces a placebo, and the efficacy of the vaccine in preventing the disease or its complications.
That is, it is in stage 3 that the first term that we want to clarify today is determined: the efficacy of a vaccine.
The fundamental concept for understanding the efficacy of a vaccine is knowing that phase 3 studies are governed by highly controlled research protocols, in which researchers carefully choose study participants.
In other words, in order to have a homogeneous population and to facilitate the comparison of the results, the participants in the phase 3 studies are more or less selected people, from which pregnant women, children, very people are often excluded. elderly or with pre-existing diseases.
At the conclusion of the phase 3 study, the number of cases of the disease that occurred in the group that received the vaccine and in the group that received the placebo was compared, concluding that the vaccine is effective if the cases of disease that occurred in the group that received the received the vaccine are much lower than in the group that received the placebo.
For Pfizer / BioNTech, for example, its efficiency has been calculated at 95% and for Moderna, 94.5%, taking that of AstraZeneca is by 82.4%, and for Johnson & Johnson, 72% in the United States66% in Latin America and 57% in South Africa.
What is the effectiveness of a vaccine?
Effectiveness is a completely different concept and involves the use of the vaccine in real life. That is, outside of a research study.
Recently, studies on the effectiveness of vaccines have begun to be published. The first of which came from Israel, a country that in addition to actively vaccinating its inhabitants is studying how much vaccines work, that is, their effectiveness.
In one of them, researchers from the health plan Clalit de Israel studied 1.2 million vaccinated people, of whom 600,000 received two doses of the Pfizer / BioNTech vaccine and 600,000 did not, comparing the frequency of symptomatic cases of covid-19 and severe cases of the infection.
Compared with the unvaccinated, the frequency of symptomatic disease was 94% lower and of severe disease, 92% less in vaccinated people, compared to the unvaccinated.
Those numbers, 94% and 92%, are called vaccine effectiveness, not efficacy.
The difference then is that the efficacy is calculated in a controlled clinical trial in which the type of volunteers are chosen to participate, and the vaccine is compared against a placebo. While the effectiveness is calculated by vaccinating all types of people in real life, and the vaccinated are compared against the unvaccinated.
Understanding the difference between efficacy and effectiveness, it is also very important to understand that none –– neither efficacy nor effectiveness–– reaches 100%. In other words, there is no 100% effective or 100% effective vaccine.
What happened in the United States?
Returning then to the news that there had been 5,800 cases of covid-19 in vaccinated people, it is very important to know that those cases occurred among approximately 66 million fully vaccinated Americans as of April 8.
Doing a simple calculation, we see that those 5,800 cases represent 0.009% of the 66 million vaccinated. Which means that the disease did not occur in 99.991% of those vaccinated.
Regarding the characteristics of the 5,800 cases, the CDC reported that just over 40% of the infections occurred in people over 60 years of age, 65% in women and 29% were asymptomatic cases, being something new –– and different from the cases described in Israel–– that not all patients developed mild illness.
Knowing that there are variants of SARS-CoV-2 that may not be sensitive to the neutralizing antibodies produced by vaccines, the CDC reported that they are monitoring reported cases to group them by patient demographics, geographic location, time since vaccination, type vaccine or lot number and lineage of SARS-CoV-2.
And finally, in relation to the 396 hospitalizations and 74 deaths that occurred in vaccinated people, and taking into account that every human life is precious, it is easy to calculate and assess the number of hospitalizations and deaths that would have occurred in that group of 77 million people. people if they had not been vaccinated.
Do you have questions about the coronavirus?
Send me your questions on Twitter, we will try to answer them in our next episodes. You can find me at @DrHuerta.
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If you have any questions you can send it to doctor Elmer Huerta via Twitter. You can also go to CNNE.com/coronaviruspodcast for all episodes of our podcast «Coronavirus: Reality vs. fiction”.