Wednesday, August 4

The delta variant removes group immunity and forces more population to be vaccinated


European citizens are obsessed with a figure: 70% of the population vaccinated with the complete regimen. It has been months since the leaders of the EU committed to reaching that percentage before the end of the summer of 2021, and in Spain we are approaching it: we are going for 46.7%. The barrier is 70% because it is assumed that with that percentage group immunity against COVID-19 is achieved, that is, there are so many people protected that the virus no longer has a way to circulate and, although it continues among us, it no longer it’s so dangerous. With the delta variant entering the scenario, the calculation could change and more percentage might be required to achieve this effect. But experts warn that in reality that 70% was never a closed number, and that it will be necessary to get more people vaccinated, with delta, or with alpha, or with other mutations. In other words, the immunization campaign must continue.

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Alpha is the predominant variant right now in our country (it originated in the United Kingdom, the WHO recently changed the nomenclature). Delta accounts for about 12% of sequenced cases, although Health admits that it could be more – communities like Madrid already consider it the dominant one – because the system has many limitations. On the other hand, the calculation of group immunity is made from the number R0. The R0 is “the average of secondary cases that an index case generates in a context of zero control measures,” explains preventive medicine specialist Mario Fontán Vela. For example, in April 2020 it was considered that the R0 for SARS-CoV-2 was between 2 and 3. And from that data, with a statistical calculation, it is calculated that this R0 number corresponds to a percentage of immunized of about 70%.



A first problem is that with alpha, which expanded in January, the R0 would have roughly doubled, while with delta, it seems to have grown even more. The scientific community has not yet specified how much, but some calculations from Imperial College place the R0 of delta around 8. Other studies, such as those from Public Health England, they point out, based on other indicators (the secondary attack rate, TAS) that, in reality, delta would not be much more transmissible than alpha. But in any case, both would need slightly more than 70%, which was an estimate for the first variants.

A second problem to get the percentage: R0 is not everything. “There are two more postulates in addition to the R0 number that are not fulfilled for SARS-CoV-2: one, immunity is not 100% in all those vaccinated or infected, because the vaccines are not 100% effective; another, the disease is not distributed randomly, there are biases by age or sector “, indicates Pedro Gullón, member of the Spanish Society of Epidemiology.

And the main problem is that epidemiologists and vaccinologists already pointed out that 70% should not be taken literally. In any moment. “70% was a theory that did not have such epidemiological criteria, it was more political. Setting percentages is ridiculous, we have to know that the ideal would be to reach around 85% or 90% of the population. Whatever variant it may be. And then, we will see if we have achieved it. Before, everything is cabal. It depends on so many factors that it is impossible to say when group immunity will be achieved “, says José Antonio Forcada, president of the Nursing and Vaccine Association. He and other experts have also always pointed out that the priority was, as we have already done, to vaccinate the vulnerable, over obsessing over those high percentages.

“The more people we vaccinate, the better”

His colleague Amós García Rojas, president of the Spanish Vaccination Association and advisor in the Ministry’s Vaccine Report, agrees. “Beyond any variant, and the way the yard is, the more people we vaccinate, the better. Only then will the transmission break. We don’t have to get bogged down at 70%, we have to go further. With alpha and delta “. García Rojas refers to recent studies that conclude that both doses of Pfizer / BioNTech or AstraZeneca / Oxford are needed to protect against delta, but that with that double guideline it is enough. But for this reason, he says, we must accelerate and reach those high percentages now.

It also mentions that, as long as all countries are not protected, and in Africa some are below 3%, we will continue to be susceptible to future variants. Pedro Gullón agrees: “The more, the better. There is no point, the possibility that there are cases decreases little by little.” “We know that if more is transmitted, the threshold will be higher”, Fontán Vela ditch on the variants, but “we will know when the pandemic is controlled when the data tell us, not calculations based on assumptions that we know are never fulfilled”, Fontán Vela ditch.

Fernando Simón, director of the Center for the Coordination of Health Alerts and Emergencies, acknowledged this Monday that the estimate of group immunity could rise to a higher percentage. It could stay at 75-80%, counting people who develop “vaccine failure”, for which you also have to give a little more margin. But “we are managing to vaccinate much more than that, the oldest around 100%”, so he was not concerned.



Will we get to that 90%?

The response of the Spanish citizens so far has been exemplary, almost 100% of those over 70 years have attended the appointment of the vaccine, something that other European countries have not achieved. Even so, “it is not correct to say that there is group immunity among the elderly because it does not occur by age, it occurs at the population level. Yes we can say that the elderly are protected and that the film has changed a lot, there is already a first control of the pandemic because the virus no longer causes the lethality of before “, clarifies García Rojas. So the question is: will we continue at this rate and reach that 90% of the general population, at least among adults as long as vaccines are not authorized in minors?

“There is no other remedy. I neither see it nor fail to see it: we have to go for it. We have to convince young people, win them over to the cause, I am worried that they are being excessively criminalized. Foolishness is not associated with age is associated with other factors, and we have to explain to them that to regain our old life they have to be vaccinated, we are not going to convince them by calling them fools “, answers García Rojas. It refers to the high rates of infections that occur among those under 30 years of age, who have not yet been massively vaccinated but who are beginning to hit these weeks. “It is what remains ahead of us, those under 30 are many, and then those under 16. They are an important group because they have more mobility and social relationships,” Forcada ends.



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