Sunday, May 16

The new vaccine dilemma: how to use it to save more lives | Science


A nurse administers a dose of the Pfizer vaccine at a residence in Leganés, this Tuesday.
A nurse administers a dose of the Pfizer vaccine at a residence in Leganés, this Tuesday.Bald Elm

The slowness in vaccination against covid has plunged the world into a new dilemma in which for now there are no certainties: is it better to give the vaccine strictly following the criteria with which they were created or is it better to give only one dose to the largest number possible for people to try to save more lives by delaying the second injection?

For now science does not have clear answers. Each country will have to make difficult decisions with limited information and in the midst of a pandemic that threatens to worsen.

The situation is especially critical in the United Kingdom, a country where the incidence of covid has doubled in a few weeks, possibly associated with a new variant of the coronavirus that is probably more contagious. This is already the country with the highest mortality from covid-19 in all of Europe.

The British Government has decreed the closure of schools and a stricter confinement. Like Spain and other European countries, the UK is having a lot of trouble vaccinating the expected number of people. Faced with this situation, the country has decided to take an unprecedented step: instead of administering the vaccines in two doses with a fixed period of 21 days – in the case of the BioNTech vaccine – it has decreed that a first dose will be given to the largest number as many people as possible and the second will be delayed for up to three months.

BioNTech and Pfizer acknowledged yesterday that they have no proof that their vaccine can protect against infection if the two doses are not administered.

The idea is to achieve at least some immunity to the virus in the largest number of people at high risk of severe covid, thereby postponing a full immunization. The consequences of this decision are totally unknown, since the 95% efficacy demonstrated so far is based on the administration of the two doses with that interval of 21 days.

The same dilemma already overwhelms other European countries, including Spain, where for now the vaccination criteria have not changed. Germany, another country heavily hit in the second wave, is considering it and Denmark has already approved delaying the second dose for a month and a half, Reuters reports.

BioNTech and Pfizer, the two pharmaceutical companies that have developed the first approved vaccine against covid, said in a statement yesterday that they have no proof that their vaccine can protect against infection if the two doses are not administered. “There is no evidence that the vaccine is effective 21 days after the first dose,” they highlighted.

Epidemiologist Stephen Evans sums up the situation. “The idea that there is a valid and clear answer to this problem is false, because we see respected scientists differ on the subject”, highlights the epidemiologist of the London School of Hygiene and Tropical Medicine in statements to Science Media Center. Not even Katalin Karikó, the mother of the BioNTech vaccine, offers certainty: “We have to trust the experts who are analyzing the clinical data,” he explains to this newspaper.

But data on the efficacy of a single dose are practically non-existent According to the latest data published by BioNTech, the first dose provides 52% efficacy 12 days after the injection. It is a modest efficiency and, above all, it is not known how long it lasts in time. In contrast, a single dose of the AstraZeneca and Oxford vaccine, already approved in the United Kingdom, would be 80% effective, according to the British Government.

The British Society for Immunology released a statement yesterday supporting the decision to delay the second dose to save more lives. British immunologists argue that with what is known about the BioNTech vaccine and what is already known about other vaccines, it is an acceptable decision, although the ideal would be to follow the vaccination criteria established by the manufacturers. “We have to protect the greatest number of vulnerable people from severe covid in the shortest time,” they say.

Today, two studies based on epidemiological models have been published that show that this is the measure that can prevent more serious infections in the US But in this country, also heavily affected by COVID, another solution has been suggested: diluting the doses of the Moderna vaccine and give only half at a time, explained Moncef Slaoui, head of the state program for rapid development of the covid vaccine, Reuters reports.

The US Federal Drug Agency censured this possibility in a statement warning of the unknown risks of changing dosage or administration times without testing. There is data suggesting that the duration of immunity provided by the vaccine depends on the intensity of the immune system’s reaction after the two established doses. Change vaccination protocols “without scientific evidence can be counterproductive to public health”, They argue. “If people do not know how protected they are, more damage can be caused, as they can assume that they are immunized when they are not,” the agency highlights.

In Spain, the Ministry of Health rules out for now altering the times of administration of injections. The European Medicines Agency is on the same line: no more than 42 days should pass between the two doses, it said in a statement.

Spanish immunologists are categorical. “They are hasty decisions that are not based on scientific data but on logistics criteria and poor vaccination planning”, highlights Marcos López, president of the Spanish Society of Immunology (SEI). “Delaying the second dose a few weeks might be acceptable, but three months may be too long,” he adds.

“I don’t understand why these unproven approaches are being considered when they have tools that have proven their effectiveness, such as confinement for a period of two or three weeks,” highlights Carmen Cámara, an immunologist at Hospital La Paz (Madrid) and member of SEI.

“It is not a good idea to dilute the vaccine,” explains Africa González, an immunologist at the University of Vigo and a member of the SEI. “It may not give a good immune response especially in older people. In fact, in the influenza vaccine for those over 65 years of age, four times the standard dose is used, or adjuvants are used, to obtain a good response due to immunosenescence [envejecimiento del sistema inmune]”, He highlights.

What saves lives is not the existence of vaccines, but the practice of vaccination

Isabel Sola, a virologist at the CSIC who participates in the development of a vaccine against covid, believes that in a critical situation, protocols should be followed with people at higher risk. “The results of phase 1 of Moderna’s vaccine showed that a single dose elicits a minor, but still acceptable, immune response. The problem is that these data are from people between 18 and 55 years old. The level of protection or the duration of this is not really known, so the logical thing is that if you have to do without one dose or delay the second, it should be done with the youngest population, not with the oldest and most vulnerable, “he says.

The division of opinions is also evident in our country. Vicente Larraga, a scientist at the CSIC who is developing another vaccine against covid, believes that delaying the second dose makes sense. “Several possibilities can be considered. If it is a short time there would not be great differences in protection. Delaying the second dose could reduce the effectiveness, but not necessarily. After the first dose there are already memory cells that will be activated in any case with the second dose. Maybe at a somewhat lower level, but not necessarily. I would do the same as the UK. It is better to have more people vaccinated even if the protection percentage is lower ”, he concludes.

This dilemma is not caused by the vaccine itself, but by the problems of distribution and planning to give all available doses, with health systems already very fatigued and almost at the limit due to the rebound of the pandemic in many countries. This has resulted in far fewer vaccinations being administered than are ready to be shot. This proves an old saying in public health, explains today an editorial from Annals of Internal Medicine: what saves lives is not the existence of vaccines, but the practice of vaccination.

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