Faced with the skyrocketing number of infections caused by the Delta variant of SARS-CoV-2, and signs that the immunity triggered by COVID-19 vaccines could fade over time, some countries are considering administering booster dose to people who are already fully vaccinated.
Germany and Israel have already announced plans to administer that third dose, and a growing list of countries, including the United Arab Emirates, China and Russia, have already even started administering additional doses.
Isn’t the third dose backed by science?
Many scientists consider that the arguments to support booster doses of the COVID-19 vaccine are still very slim.
They think that it may not be necessary for most people and that it could leave millions of people who need vaccines without vaccines.
What’s more, on August 4 the World Health Organization called for a moratorium on booster doses until at least the end of September.
- “Wasting resources on reinforcements for those who are already protected against the severe version of the disease does not make much sense. Later we will probably have to think about it, but at the moment we do not have solid arguments to make that decision. Especially with what can affect those who are not yet vaccinated.
Says Laith Jamal Abu-Raddad, an infectious disease epidemiologist at Qatar’s Weill Cornell Medicine in Doha, reaffirming the idea that we don’t know whether a booster dose would actually have any real benefit.
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A debate between prudence or security
It is what we are in. Because many other scientists think that although it is true that we still do not know enough, while the Delta variant is conquering some countries and appearing in others, health authorities cannot afford to wait for the definitive answers to decide on the application of the booster dose.
So the decision will likely have to be made without having the full evidence.
What do the booster doses do?
As almost everyone knows by now, vaccines produce an increase in the number of immune cells responsible for producing antibodies that then slowly decline.
But they also generate a small group of B cells, which will be responsible for generating more antibodies, and T lymphocytes, which are the “killer cells” whose function is to seek and destroy infected cells.
What a booster dose does is elicit stronger immune responses.
How?:
By multiplying the antibody-producing B cells, which will again raise the levels of protection against the pathogen.
And although with time their number will decrease again, as the memory B cells that remain will be larger than those that were, we will be prepared to give a faster and stronger response to subsequent exposures.
Furthermore, through a process called ‘affinity maturation’, the antibodies they produce will bind to pathogens more strongly, increasing their potency.
Can COVID vaccines stop transmission?
Few trials have been done on booster doses of vaccines, but those that do exist agree that both Moderna and Pfizer-BioNTech, Oxford-AstraZeneca and Sinovac’s vaccines work.
That is, they caused an increase in the levels of “neutralizing” antibodies that block infection, when they were administered several months after the second dose.
Now a trial is also underway in the UK to see if boosters and different brand vaccines can be combined. And studies suggest they could even produce stronger immune responses.
These trials also suggest that the side effects of the third dose, such as headache and fever, are very similar to those seen with the previous doses.
Do we know that immunity from vaccines is waning?
First impressions suggest that the levels of antibodies elicited by most COVID-19 vaccines are decreasing over time.
But what scientists do not know is if that also means a decrease in protection against the virus.
Because we do not yet know what level of neutralizing antibodies is necessary to affirm the effectiveness of the vaccine. They are looking for what is known as a correlate of protection.
- “We don’t really know what that magic number is & rdquor ;.
- Knowing it would allow researchers to determine more precisely if and when a boost is needed. But without having that correlate correctly defined, it is difficult to say if we really need this booster dose.
Are those who were vaccinated the longest less protected?
There is no sufficiently proven answer to make decisions with confidence. But there are studies.
- Last month, Israel’s Ministry of Health estimated that from December 2020 to July 2021 the vaccine’s protection against infections and diseases had decreased from being above 90% to staying at 40%.
But this figure could be due exclusively to the effects of the Delta variant.
- Another study, conducted by researchers at Pfizer – BioNTech, who have pushed hard for booster doses to be given, showed that the efficacy of the vaccine against symptomatic disease had dropped from 96% to 84% after 6 months.
- And Moderna, in a statement in April, put the efficacy of its vaccine at more than 90% after half a year, compared to its original efficacy figure of 94%.
These are data that can be altered by multiple factors, but that can serve as sufficient evidence.
Are infections between vaccinated people a warning sign?
It is clear from the trial data that protection against serious diseases remains high.
- Pfizer – BioNTech and Moderna estimate that the efficacy remains above 90% against severe Covid-19, after 6 months.
- And real-world data, obtained in Israel, the United Kingdom and elsewhere, suggests that vaccines are enormously effective in keeping people out of the hospital, even when the cause is the Delta variant.
Vaccines were developed largely with this goal in mind, but & mldr;
- “What we are not clear now is whether these mild infections that are spread among vaccinated people could be the harbinger that we are losing protection. Are they an early warning sign? That is what we do not know.
We must weigh the unvaccinated
If we are still not clear about the benefits it brings, we could say that the booster dose is a real risk for the many unvaccinated people who are going to miss their first dose.
That’s why scientists insist that giving a booster dose in the coming months can be a waste of resources, both globally and nationally.
Because a small reduction in effectiveness does not justify someone without major problems receiving a third dose when many other people have not even received the first.
As researcher Abu-Raddad says:
- “We don’t have clear evidence that there is enough loss of efficacy to shift our focus or distract us from the main goal, which is to try to get the first doses to as many people as possible.”
But not all countries think the same.
- The US after initially rejecting the idea of third doses, now appears to be considering them.
- Israel announced plans on July 29 to give people over 60 a third dose of the Pfizer-BioNTech vaccine.
- The UK has drawn up tentative plans to offer vaccines to those over 50, as well as other high-risk groups, starting in September.
In any case, and although opinions are divided, many scientists believe that given what we know right now, the booster dose could be a luxury item in a world in which millions of people are hungry for vaccines.