A woman receives a dose of the vaccine in Guadalupe, Nuevo León.DANIEL BECERRIL / Reuters
The most contagious mutation that SARS-CoV-2 has produced is entering the Latin American continent through its northern border. The first cases of the delta variant in Mexico became known in early May. And, although for weeks the number of known cases numbered in the dozens, it is already the dominant version of the virus in Mexico City, the area most affected by the pandemic in the entire country. The strain moves fast. The epidemiologist Gustavo Olaiz estimated that by the end of August, nine out of ten cases would be of this variant, but the change is occurring much earlier than expected. "It is already with us, it is dominating now," says the director general of the Center for Research on Policies, Population and Health of the UNAM. Delta is at the center of the third wave of infections,with young people and people who have not been vaccinated as the main protagonists.
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This trend is already being reflected in the regional key data. In the last four weeks, more than half of the samples sent by Mexico to GISAID, the reference entity in the collection of world data on the genetic evolution of the virus, are identifiable as delta: about 528 in total. Only Brazil has a higher proportion, and this is probably due to the fact that it has fewer samples registered in total: this metric is not as precise as one might wish, because it depends enormously on the number of observations made and reported by each country. In recent times, Mexico maintains one of the most complete reports. This does not mean that delta is overrepresented in its samples, but more likely that it is undercounted in those of its neighbors. In any case,the variant is already in a majority of the nations of the continent.
Nothing too different could be expected, given the ability of delta to be more contagious. It is this ability that would have allowed it to become strong in the UK or India, and now in various corners of Europe (including Spain, where 72% of the samples reported to GISAID in the last four weeks are delta), but also in the US (68%). Every time the virus jumps from one body to the other, chance has the opportunity to roll the dice and modify some of its DNA, and when one of these mutations expands and manages to establish itself as a variant, it is usually precisely because it shows some kind of advantage. competitive against its predecessors. "This sudden increase, the second in importance and which caused us to have more cases than at the beginning in Mexico, is due to the variants that are arriving,especially the delta, they are clearly more contagious ”, explains Olaiz. "That is what is happening all over the world, the most transmissible variant is the one that is 'winning' over the others," adds the specialist.
The specific measure of that advantage, how much more contagious delta is, remains under study. It is plausible that it depends in no small measure on the context in which it takes place, and the Mexican has already shown evidence of favoring contagion. This is particularly true in areas of high urban density, or those with the highest potential number of possible insertions of imported cases. Mexico City meets both conditions, which would help explain the strong increase in infections that the city is experiencing. His Secretary of Health, Oliva López Arellano, announced since last week that delta was the "dominant" in the capital.
The enormous accumulated incidence of SARS-CoV-2 has not served as a retaining wall, possibly because the greater contagion capacity of delta helps it spread among a population still susceptible to a first infection, and perhaps because it produces more reinfections: although it is not There are sufficient data on second infections in Mexico, the immune escape power of delta is known. It remains the hope that this acquired immunity will act as a lethality reducer for the virus, together with the fact that for now the new wave is focused on the youngest. But in recent weeks, deaths have already begun to rise with the usual delay in cases. "We have to understand that delta is not a variant that is lower in terms of the risk of serious illness and death," insists Olaiz.
For this reason, the target of the messages of the Mexican authorities are young people, who in the previous stages of the epidemic seemed to be the least likely to be infected. "Most of the people with covid at this time are under 50 years of age and the vast majority were not vaccinated, more than 90%," said the Undersecretary of Health, Hugo López-Gatell last Tuesday. "It is important that all of you who are young take into account that you too can be affected and affected," urged the Mexican spokesman for the pandemic.
With a year and a half of restrictions and calls with uneven success, and taking into account the imperfect immunity acquired by previous infection, the only solid barrier that is known against delta is vaccination, in Mexico as in the rest of the world. Several of the vials most used in the country are known or suspected to work against the new variant: data from the United Kingdom confirm the high effectiveness of those produced by Pfizer and AstraZeneca, once the two corresponding doses have been administered. Johnson & Johnson said in a statement earlier this month that its vaccine, which was applied along the border with the United States, was effective for this version of the virus. Shortly before, Gamaleya assured at the end of June that his Sputnik V also maintains a high power against delta,although without revealing more than the data of 90% reduction in the probability of contagion. Of those of Chinese origin (Sinovac, Sinopharm) for now, it is hardly known that - like all the previous ones - they present a comparatively lower antibody response against delta, but without the defenses disappearing, and nothing among the experts anticipates a complete loss or massive protection.
With six options in its portfolio, vaccination in Mexico seeks a greater acceleration than that of the rest of countries of similar size in Latin America (particularly Brazil), without achieving it.
"We are in an arms race: we have the vaccines and the viruses, the mutations," said Alejandro Sánchez, a researcher at the UNAM Institute of Biotechnology, a month ago.
At the current rate of vaccination, delta could beat Mexican immunization.
"You have to make an effort to push vaccination, especially in second doses," says Olaiz, "we have to tell people that one dose is not enough."
The other pillar to defeat this variant is in social behavior, although the Government has discarded new restrictions and is reluctant to reverse the economic and social reopening.
"We certainly have a tired, fatigued society of having these long months of epidemic, what one can ask of society in terms of reduced mobility is not the same today as it was in February 2020," he justified López-Gatell.
"We must not lower our guard.
It is understood that people are tired, but it is better to be tired than to be sick, hospitalized or dead, ”says Olaiz.
"That is the message we have to send to everyone."
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