Do i need a second dose?


In full debate on whether the general population will need a third dose Of the RNA vaccines against COVID-19 (Pfizer and Moderna), those vaccinated with Johnson & Johnson (Janssen) have long wondered if they will get a second one. This week, the Vaccine Report proposed to the Public Health Commission the possibility of a booster dose after the appearance of outbreaks among prison inmates, immunized with it. So far no decision has been made on this matter, but is this reinforcement necessary?


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Johnson & Johnson introduced its vaccine as a single dose, but started a clinical trial with two doses in November 2020. The latter did not surprise immunologists: the adenovirus-based technology is the same as that of AstraZeneca and Sputnik V, both two-dose. Many were clear from the beginning that Janssen would end up offering the second. The volunteers and volunteers who participated in the trials of the pharmaceutical company in Spain, in fact, received both.

“It was surprising that it was only one dose, because vaccines usually need one [segunda] to give a good enough response both in quality and quantity “, Salvador Iborra, the immunologist from the Complutense University of Madrid, explains to elDiario.es. He clarifies that this reinforcement paves the way generated with the first:” The lymphocytes that you have they only increase in number, but reach a higher level of maturity and affinity for the antigen. ”

The immunologist from the University of Valladolid Alfredo Corell already shared with this newspaper in May a similar opinion. “In the race to immunize as soon as possible as many people as possible they have positioned themselves very well because it has been sold as the only one dose, but everyone in the scientific world knew that in the long term it would be two,” he said then.

The Johnson & Johnson single-dose was a great advantage in a context of vaccine shortages and urgency to reach the largest possible percentage of the population. “It went very well with the stoppage of AstraZeneca and the lack of doses of Pfizer and Moderna, but I think that this advantage that it had at the beginning now is its weakness,” says Iborra.

In Spain, about two million people have received the Janssen vaccine. This began to be given to people over 70 years of age, an age that gradually decreased to 40. On the other hand, it has been offered to vulnerable or difficult to vaccinate groups: unregulated immigrants, homeless people, psychiatric patients, prison inmates … However , in some places it has also been used with people who had already passed COVID-19 and even in people over 18 years of age who, in theory, did not meet the necessary requirements for the single dose. In short: many people waiting for studies and experts to comment.

What the data say

Janssen’s vaccine was less effective than its competitors from clinical trials, although it is true that it is not possible to compare analyzed vaccines with different experimental designs carried out in different populations and times. Even so, this difference has been maintained in studies carried out to estimate the effectiveness of vaccines under real conditions.

The data for Janssen is more statistically noisy than its competitors. Their confidence intervals – the range of figures between which the true value lies – are much wider and there is greater variation between countries. However, the percentages of effectiveness are always lower when it comes to avoiding infections and hospitalizations.

A recent study published in the magazine NEJM, carried out with people over 50 years of age between January and June 2021, calculated an effectiveness for the Johnson & Johnson vaccine of 68% in preventing hospitalizations and 73% in preventing ICU admissions. In comparison, these percentages were 90% for mRNA vaccines and remained at 80% in those older than 85 or with previous pathologies.

A report published by the CDC With data pertaining to summer 2021, already with delta as the dominant variant, it shows an effectiveness against hospitalizations of 60% compared to 95% for Moderna and 80% for Pfizer. Although Janssen’s confidence interval ranges from 31% to 77%, it never reaches that of its competitors. In this case, it is about revenue avoided per case, so the data is biased downward for all vaccines.

More data, these from the netherlands, also show that Johnson & Johnson is somewhat behind the rest: 87% effective in avoiding hospitalizations, behind Pfizer (92%), AstraZeneca (93%) and Moderna (95%). In South Africa, data shared so far from a study with some 480,000 health workers shows 71% effectiveness against delta in avoiding hospitalizations.

What the experts say

American journalist Steve Usden I asked a question on the third doses that could well be applied to this issue. He asked to know “if the data supporting the effectiveness of a booster dose are so compelling, and the need so urgent, that the decision must be made now, or if it can be postponed until evidence is collected for a long period of time.” .

The president of the Spanish Association of Vaccination (AEV) and head of Epidemiology of the Canary Islands Health Service, Amós García, asks to wait for “solid scientific evidence” before making a decision. “It is logical to open the debate and be aware, especially in certain profiles, on whether or not to administer this booster dose,” he explains to elDiario.es. He assures that there are “several studies in progress” that will offer more information in this regard.

“I consider that it is preferable that they administer it, a second dose seems reasonable to me, it is not crazy,” says Iborra. It is based on the preliminary results of the Johnson & Johnson clinical trial studying the second dose, shared at the end of August, in which the neutralizing antibodies were observed to increase nine times. The study, however, has not yet been completed and its final results have not been published.

“I think it is a mistake to pose it as an emergency,” says preventive Mario Fontán, who asks not to fall into a scenario of “vaccinate to vaccinate.” He believes that the debate is similar to that of the third doses, and that the important thing from the point of view of public health is “to vaccinate as many people as possible to avoid collapse and serious illness. We are achieving that.”

To complicate matters further, the question of what second dose would be applied. Although studies with heterologous guidelines have so far shown very good results when combining adenovirus vaccines with RNA vaccines, Iborra believes that the logical thing is to follow what clinical trials dictate and give a second one from the same manufacturer.

The need for a population view

None of this is to say that those vaccinated with Janssen, or some of them, should not receive a second dose at some point. “It can be considered in vulnerable groups if effectiveness against serious conditions is lost, but when analyzing it we must look at what protects most at the population level, whether to vaccinate unvaccinated people and promote campaigns in other countries or add doses to already immunized people that presents good figures “, continues Fontán.

Iborra clarifies that, for the moment, the loss of effectiveness against serious pictures does not seem “dramatic”. Therefore, he assures that we do not know if outbreaks like those observed in prisons “they will lead to pathologies“.

That is why Fontán asks not to raise the debate from an individual or nationalist point of view: “Some groups or individuals will always have less immunity than others, but if I have Janssen and my environment has Pfizer, I benefit from their protection because we all benefit from that we are all vaccinated. ” He considers it a mistake to pose the question as a “detriment” in which there are people with three doses and others with one. He thinks that talking about better and worse vaccines is “cheating.”

“As long as a person has not received the vaccine that seems to be giving better results, he will be able to say that he wants a booster with that one,” he adds. “They are First World arguments, where we can choose. It is very individual to consider it as receiving a better or worse vaccine, when the issue is that we are all protected.” What matters is that, so far, people vaccinated with Janssen have high protection against severe COVID-19. Especially in those countries, like Spain, that have high levels of immunization.

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