Why is it necessary to receive the 2 doses of the vaccine against covid-19?

Dr. Huerta analyzes new guide on the use of masks 2:32

(CNN Spanish) – The vaccine against covid-19 requires, in some cases, two doses to provide adequate protection against the disease. However, some people choose to receive just one.

Do we really need to get two injections? Dr. Elmer Huerta explains the rationale behind the scientists in this episode.

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.

Today we will see two frequent concerns related to the second dose of the covid-19 vaccine. The first is whether the second dose is necessary or not, and the second is whether that second dose can be spaced out for some time.

First of all, let’s remember that most of the COVID-19 vaccines available so far in the world require two doses. The exceptions are Johnson & Johnson and Cansino.

The vaccine against covid-19: do I have to receive the second dose?

In that sense, a recent report from the United States Centers for Disease Control and Prevention (CDC) reported that the proportion of people who received the first dose of the Pfizer / BioNTech and Moderna vaccines and did not return for the second dose more than doubled between March and April. In March it was 3.4% and in April it was 8%, which is equivalent to more or less 5 million people.

That can be a consequence of having a vaccine that requires two doses, such as Covid-19. It is not uncommon for vaccines that require two doses to not apply the second to people who received the first.

In the case of the vaccine against shingles or herpes zoster, for example – which also requires two doses with an interval of between two to six months in people over 50 years old – it has been seen that 26% do not apply the second dose.

Having nearly 5 million people who have not completed their covid-19 vaccination is worrisome because it decreases the chances that society will achieve group or herd immunity.

Why are there people who do not get the second dose?

On the other hand, it is very important to ask why so many people have not had the second dose of the vaccine.

Is it a lack of information and to believe that one dose is enough? Is it a consequence of false news that may be circulating in the community? Or is it possible that the data is not accurate, since the vaccination points are electronically disconnected. It is possible that many people received the second dose, but it was not registered in the database? Or, finally, what barriers exist for people to apply the second dose?

Obviously each of these possibilities needs a different correction strategy.

The analysis of this trend through a survey

As for many people falsely believing that a single dose already gives them the protection they need, a recent survey published in The New England Journal of Medicine on April 28 sheds some light on this.

The survey, representative of the United States population, was conducted among 1,027 adults between February 11 and 15, 2021, and tried to find out – among other things – the public’s knowledge about when the vaccine protects the vaccinated .

The results were surprising:

About 20% of those surveyed believed that after the first dose the vaccines were already capable of giving strong protection to vaccinated people, and 36% were not sure.

That is, more than half of the respondents did not have good information.

Only 44% of people said, correctly, that a week or two after the second dose the vaccines provide strong and solid protection.

It is therefore important to reinforce the knowledge that the second dose is essential to achieve complete protection.

Why is the second dose of the covid-19 vaccine important?

In this regard, in a recent presentation at the White House, the director of the National Institute of Allergy and Infectious Diseases of the United States, Dr. Anthony Fauci, reviewed recent scientific publications on the importance of receiving the second dose.

For example, he mentioned a recent Israeli study that showed that the second dose of the Pfizer / BioNTech vaccine raised protection from severe COVID-19 from 62% after the first dose to 92% after the second. That same study said it raised the protection from being hospitalized for COVID-19 from 74% after the first dose to 87% after the second.

He also cited another study that showed that the Pfizer / BioNTech and Moderna vaccines reduced the chance of hospitalization in people 65 and older from 64% after the first dose to 94% after the second.

Dr. Fauci also cited a study that we described in the March 25 episode that the chance of becoming infected with the new coronavirus was 36 times lower in people who received two doses of the vaccine, compared to those who received only one.

The second dose of the vaccine and variants

Another very important study, cited by the specialist, found that after the second dose of the Pfizer / BioNTech vaccine, the volunteers produced a greater amount of neutralizing antibodies against the B.1.351 variant, identified in South Africa, compared to those produced after the first dose.

This is important because, since there is a fear that this variant has less sensitivity to current vaccines, a second dose ensures that the vaccine can work.

In summary, the second dose of a vaccine is very important and we believe that a greater number of information campaigns in different languages ​​and segmented groups of the population on the usefulness of a second dose of vaccines is necessary.

We agree with Dr. Fauci that vaccination programs should make it easier for the public to receive the second dose, scheduling it at the time of giving the first dose, sending reminders in text messages to people who have not yet received the second dose, and rescheduling the doses. cancellations, making it very easy to change the time or date of that second dose.

As for how long it can take to apply the second dose, good news:

The CDC says that if for some reason the 21st day for Pfizer or the 28th day for Moderna cannot be met, the second dose can be given up to six weeks or 42 days after the first.

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.

If you think this podcast is useful, help others find it by rating it on your favorite podcast app. We’ll be back tomorrow so be sure to subscribe to get the latest episode on your account.

And for the most up-to-date information you can always head to Thanks for your attention.

If you have any questions you can send them to Dr. Elmer Huerta through Twitter. You can also head over to for all episodes of our “Coronavirus: Reality vs. Reality” podcast. fiction”.

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