Thursday, September 16

Mass immunization hinders the development of a new generation of COVID-19 vaccines

Vaccination campaigns against COVID-19 throughout the world proceed at a very different pace depending on the income level of each country, and the inequality in this matter is more evident than ever. At this time, they have been administered around 5,000 million doses, with the following distribution per 100 inhabitants: while middle and high-income nations have inoculated more than 100 doses, low-middle-income countries have only administered 32, and low-income countries have only been able to distribute two dose, with a large vulnerable population still pending vaccination.

The world is making billions of vaccines against COVID-19, why are they not reaching Africa?

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Unlike the first vaccines that were evaluated in clinical trials (from Pfizer, Moderna, AstraZeneca, Janssen, Sinovac …), current experimental vaccines face multiple challenges: on the one hand, there is a high vaccination coverage in the countries developed, with more than 50% -60% of the population immunized with at least one dose, which continues to increase. Furthermore, almost all of the older people have been fully vaccinated in many of the above nations.

On the other hand, the greater availability of vaccines of proven efficacy among the general population leads to a much lower motivation to participate in clinical trials, as volunteers could receive a vaccine of uncertain efficacy. Taken together, this situation makes it difficult to find eligible participants to be able to evaluate COVID-19 vaccines and forces clinical research on these preventive tools to adapt.

To rigorously determine the efficacy of an experimental vaccine against COVID-19, it must be tested through clinical trials in unvaccinated people who have not been previously exposed to the coronavirus, compared to a group of people who receive placebo or a vaccine already marketed. As Antonio Gutiérrez, researcher and epidemiologist at the Hospital Universitario de Valme explains: “If we introduced the selection bias of patients with previous exposure, either due to having had the disease or being vaccinated, it would make it completely impossible to obtain reliable data from this We cannot know if the group that is vaccinated has a higher incidence of disease, hospitalization, death, etc., (depending on the objective we set) than the group that is not vaccinated, if both groups do not have an immune system that does not it has never been introduced to the pathogen. ”

The peculiarities of clinical trials

Current circumstances are forcing some procedures to change in clinical trials of vaccines against COVID-19. One of the key details to consider is whether the existence of the placebo group is justified in the trial. If there are vaccines of proven efficacy available in a country, there are, in principle, no ethical reasons to use placebo with the intention of ascertaining the efficacy of a new experimental vaccine except in very specific cases (children or pregnant women, for example). In Spain, for example, the pharmaceutical company Hipra has recently launched a phase I / IIa trial to evaluate the safety and immunogenicity of your vaccine consisting of a recombinant protein. Instead of a placebo group, the study will feature a group that will receive a commercially available vaccine against COVID-19 and that will be used to compare its results against the experimental vaccine.

Another strategy that is being taken to evaluate new vaccines against COVID-19 in developed countries is to select a younger population, whose vaccination percentage is not yet that high compared to the older groups. In the case of the Hipra study, only healthy adults between 18 and 39 years were included. On the contrary, this approach has the disadvantage that it prevents knowing the safety and efficacy of vaccines precisely in the people most vulnerable to suffering from COVID-19, the elderly. To solve this problem, there is the option of conducting clinical trials in developing countries, where vaccination coverage is still very low for all ages and, therefore, it is easier to access unvaccinated volunteers. In that sense, various analyzes in this regard They highlight the increasingly important role that developing countries will have in testing new phase III vaccines, even with the justified use of the placebo group, as these places have limited options to access the vaccines already on the market.

“Enhanced” and Booster Vaccines Against COVID-19

None of the currently marketed vaccines are designed to prevent coronavirus infection. That is, they do not offer sterilizing immunity. Instead, their primary goal is to prevent serious illness and deaths from COVID-19 among vaccinated people. This implies that people immunized with the vaccines can infect others if they become infected with SARS-CoV-2, although more and more studies indicate that their contagion capacity is much lower than that of unvaccinated people.

In the long term, the ideal for everyone would be to have vaccines that allow the development of sterilizing immunity, since they would not only protect against COVID-19, but also prevent contagion from vaccinated people. This would be a great advantage in controlling the pandemic. Antonio Gutiérrez points out some vaccines in development that seek precisely this objective. Among them, the one being developed by the CSIC in Spain, for intranasal administration, and in which the virologists Luis Enjuanes, Isabel Sola and Sonia Zúñiga are involved. Gutiérrez adds that “Cansino has already published the results of his phase I clinical trial of its aerosolized viral vector vaccine. “The objective of both vaccines is to block the passage of the coronavirus into the body through the nose and thus prevent infection.

One of the biggest unknowns behind current vaccines is how long their protective capacity against COVID-19 will remain. To shed light on this issue, there are several ongoing clinical trials to evaluate the effects of a booster or booster dose to boost the immune response, compared to those following the conventional regimen. In addition to this, there are also several clinical studies that are evaluating the administration of doses of different vaccines (heterologous regimen), in comparison with the conventional regimen in which two doses of the same vaccine are inoculated (homologous regimen). Although there are still details to be known, the results thrown up to now they are positive with respect to heterologous patterns.

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