The single-dose drug from Johnson & Johnson was raised until its paralysis as the great hope to accelerate immunization.

Vacuna de Janssen.  EFE / EPA / Szilard Kosztticsak

New delay in the vaccination campaign. The fourth vaccine approved by the European Medicines Agency (EMA) fmade by Janssen, the US affiliate of Johnson & Johnson, has seen its delivery in Europe delayed after the US announced an investigation after registering six cases of a rare and serious type of blood clot in people who have received this vaccine. 6.8 million Americans have already received this vaccine, and one person affected by this type of unusual reaction has died.

Spain had planned to receive up to 5.5 million vials of the drug until June, with a first batch reserved for the age group between 79 and 70 years, but it could be administered to all patients “under 80 years of age.” This vaccine has two advantages over the previous three. On the one hand, it is kept at a temperature between two and eight degrees Celsius, that of a normal refrigerator, which facilitates its distribution and handling. For the other, it is single-dose: a single ‘prick’ is enough.

Janssen is based on a different technology than Pfizer and Moderna, which are messenger RNA vaccines, an encoding of a form of the coronavirus protein S that allows the immune response to be triggered. Like AstraZeneca’s, it uses a genetically modified adenovirus to “teach” the immune system to protect itself from the SARS-CoV-2 coronavirus if infection occurs. The first three vaccines, however, have opted for the double dose even when the immunity developed after the first was already remarkable. The UK, in fact, made the risky decision to delay the second to allow for broader coverage. of departure.

“The design of the trials is based on how the immune system works. For example, most of the vaccines that are administered in the vaccination schedule to children are of at least three doses, although there are two (MMR and chickenpox) for which two doses are required and one, that of the flu, which is a single dose, to include the new strains that circulate each year, understanding that there is prior immunity against the flu virus from previous years ”, explained the professor of Immunology at the University of Vigo and former president of the Spanish Society of Immunology, Africa González, to EL ESPAÑOL.

The double dose approach, therefore, would be the ‘orthodox’, while the single dose would be the ‘battle’ approach: in the context of the pandemic, offering an acceptable threshold of immunization with a single application would reduce new infections more quickly. This, however, appears to lead to a reduction in efficacy: Janssen’s phase 3 drug was set at 66% at 28 days after vaccination, below the spectacular 95% success of Pfizer or Moderna. This, added to the fact that a risk of thromboembolism may also appear, can lead to a social rejection of this vaccine, as happened with the AstraZeneca vaccine, considering it “the bad one”.

The data, however, must be qualified. First, Janssen’s trials have followed those of messenger RNA vaccines, in a context in which variants of the coronavirus have proliferated across the planet, with different capacities to outsmart the antigen. Thus, the efficacy in Brazil was 66% and in South Africa 64%, two countries that have identified more contagious local variants, but in the US, the success increased to 72%. Similarly, a recent study in Israel suggested that Pfizer’s vaccine would be less protective against the South African variant.

On the other hand, the role of the vaccine is not only to prevent infection, but to strengthen the immune system to avoid a serious picture of the disease that endangers the life of the patient and aggravates hospital collapse. In that sense, the effectiveness of Janssen in phase III to prevent severe cases was 86%, increasing to 90% after a month and a half, and none of the trial participants required hospitalization. There were no deaths either. Therefore, even with a “one-third” chance of contracting Covid-19, the vaccine guarantees that it is the mildest variant, which can be passed at home.

“There are many things that we lack to know about vaccines. Among others, its comparative effectiveness, the duration of immunity, the real effectiveness against new variants and their side effects. What we do know is that they all manage to reduce severe cases of Covid-19. All the trials have shown an excellent effectiveness profile against hospitalization ”, writes the FISABIO researcher Salvador Peiro in The Conversation. In other words, all compensation is good, and the end of the health crisis is near. There will be more punctures in the future, when vaccines are adapted to fine-tune the shot against variants.