The possible second dose of Janssen's vaccine is something that has been in the air since they started vaccinating. Just look at the fact that the drugmaker started a clinical trial using two doses of the vaccine as early as November 2020.

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This cannot surprise us because we have already seen that with all other vaccines it is necessary to administer two doses to obtain better protection. Other vaccines that are also based on adenoviruses, such as Astrazeneca and Russia's Sputnik V, use two

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As expected from the results obtained during clinical trials, the data indicate that the effectiveness of Janssen's vaccine in preventing hospitalizations and deaths from covid-19 appears to be lower than that observed with the other vaccines that use two doses.

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Preliminary results indicate that neutralizing antibody levels increase several-fold and protection increases to levels similar to those seen with the other vaccines.

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Although these are preliminary results and it is best to wait for all the data from the full study, it seems to be clear that, although one dose of Janssen's vaccine protects against covid-19, two doses protect better. So the debate now is whether or not that improvement in protection justifies the administration of a second dose."
"One thing we cannot forget is that vaccines also limit infections and virus transmission. Therefore, although the protection obtained with one dose may be less than that obtained with other vaccines, the fact that a large part of the population is vaccinated means that this protection may be sufficient.

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At the present time it seems logical to raise the need to administer a second dose of the Janssen vaccine to obtain the maximum possible protection, at least in the most vulnerable people and those belonging to risk groups.

The data show that the second dose separated by two to six months from the first dose increases the efficacy quite a bit more. Antibodies increase fourfold [over the first dose] if you give the second dose at two months and twelvefold if you inject it at six months.

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The Janssen vaccine was getting very high efficacy with one dose, but when you give two you get 100 percent protection [against severe cases] after 56 days.
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The most important thing is that they see that after six months it also works and that it's even better than just the first dose. This implies that you could give the second dose to people who have had the first dose even after such a long time.

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Those who have been vaccinated in Spain were vaccinated less than six months ago, so now we could probably give them already the second dose.

If you give a second dose obviously the intensity of the response is going to be greater. The question: do you really need that additional increase in immune response? Maybe, most likely, no.

With the level of antibodies and cellular immunity you already have you probably don't need [another dose]. I would think we're probably in that situation with the Janssen vaccine.

Sputnik V is the same as Janssen's and has a 'lite' version that uses Ad26 (adenovirus 26), just like Janssen, and they say it's also very potent and doesn't need another dose.

As long as we don't have indications, and right now there are no indications that a second or third dose is needed, I think the effort has to be put into vaccinating as many people as possible, especially in countries that don't have vaccines.

It seems much more important to me that these second and third doses go to countries that have only 1% of the population vaccinated as long as we have no indications that the immunity we have achieved in Western countries is declining. It is a global problem and we have to try to reduce infections worldwide.

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