Immunologists Carmen Álvarez, from the International University of La Rioja (UNIR) and Africa González, from the University of Vigo, clarify to Efe some doubts that may arise about the effectiveness of vaccines against the coronavirus.
1.- What do we mean when we talk about the effectiveness of vaccines?
Effectiveness indicates protection against death and serious illness, but they do not prevent contagions, “especially against the Delta variant, which is so contagious. We can get it, but in an asymptomatic or much milder way ”, explains González.
The vaccines were designed -remembers Álvarez- to prevent serious disease and death and, when the complete schedule is in place, they are being effective in the percentage that was said, which depends on each vaccine (those of Pfizer, Moderna or Astrazeneca superior to the 90% effective) because “nothing is ever one hundred percent”.
2. – So, in some countries with high vaccination rates, for example Israel, why are hospitalizations increasing?
There are several factors, “but the most important one, surely, has been the appearance of the Delta variant, much more contagious, which has caused people already vaccinated to become infected again”, indicates González.
There are also people who were not vaccinated or in whom it was not totally effective and, in addition – he adds – there is a decrease in protection after a while, especially in older people.
Álvarez recalls that there is no one hundred percent effective vaccine. “In the event that it is 95% that leaves you 5%, which, if now the virus is more transmissible by the Delta variant, it causes more people to become infected”, which does not mean that if they have that being hospitalized end up in the ICU.
3.- To what extent are vaccines used to prevent transmission?
In addition to being effective against serious illness and death, another question is whether vaccines could also serve to prevent transmission, but since they were not designed for that, it was not known at first, Álvarez says.
With the first variants of the virus, Alpha and Beta, “they worked very well” to prevent transmission, but with the Delta “it seems that it is not working so well.” That is not effectiveness, but transmission percentage “and that is what may be failing.”
What has changed with Delta is the number of people who have to be vaccinated to “achieve a very good group immunity”, which is no longer 70%, “now we have to reach 90% of the vaccinated population, with this highly transmissible variant ”.
4.- Is it normal over time for antibodies to the virus to be lost?
When we talk about the protection of a vaccine, we refer to the entire immune system, with its cellular components and antibodies. Some studies – González emphasizes – only focus on antibodies, “when everything should be analyzed at the same time.”
Antibodies decrease normally over time; the virus has already disappeared and, therefore, they are not necessary. “The important thing is that memory cells remain, which can be activated quickly and efficiently the next time they see the virus, and a whole battery of cells and antibodies will be generated again.”
This immune memory – he indicates – is defective in some people, especially the elderly, and makes them more susceptible to becoming ill and reinfected.
5.- Is a third booster dose justified at this time for the entire population?
The World Health Organization (WHO) has requested a moratorium until October to allow sufficient doses for developing countries, “but some have already skipped it”, González highlights and considers that “the logical thing is to give a lifeline to all and not to give two life jackets to a few ”.
Álvarez points out that a third general dose is not scientifically justified. What must be achieved is that countries that have a vaccination rate of two or three percent reach, at least, 20%, although he adds that this reminder prick could be necessary for immunocompromised patients.
The European Medicines Agency (EMA) is analyzing the data, “but it seems” -says González- that a third dose would not be necessary globally, “but may be authorized for immunodeficient, or people immunosuppressed by drugs, after receiving a transplant, or older people ”.
6.- Is there a possibility that we have to continue vaccinating against covid-19 every little time?
For now, we don’t know this, González says. The Delta variant has come to compromise what had been achieved so far and “it is likely that new ones may arrive, which may require not a third dose, but a new vaccine.”
On the other hand, once most of the population is vaccinated, their immune system can learn and improve against possible new variants that arrive, points out González and concludes that “if we had not had vaccines, with the Delta variant we would have had collapse health system and many more deaths
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