Since the covid pandemic began and new variants of the initial virus emerged, each one that prevailed became "the most contagious."
Alpha was much more than the original, but less than beta, which in turn had less transmission capacity than delta, very contagious, but not as contagious as omicron.
In this evolution, the last step (for now) is the XBB.1.5, a sublineage of the latter, unofficially baptized as Kraken, which is advancing through the United States and has once again taken over the band of those who have the easiest to infect, although it does not seem to be more serious.
XBB, a fusion of two omicron variants, has been under the radar of the World Health Organization (WHO) since early December.
Two mutations of this have given rise to XBB.1.5, which has become the leading candidate to prevail worldwide after growing rapidly in the United States, where XBB and its descendant account for almost half of the cases.
The WHO has already detected it in 25 countries, including Spain, where some cases have been identified, although for now, anecdotal.
Both in the sequenced random samples and in the wastewater analyzes carried out by the Ministry of Health, a clear predominance of BA.4 and BA.5 has been found, which are the ones that have been spreading massively since last summer.
The very nature of the virus means that for a variant to become predominant, it has to be more
contagious
than the previous ones.
Otherwise, it would not be imposed on those that already circulate.
But the transmission capacity of a virus is not an absolute and isolated fact, but the result of the interaction with its hosts (human beings), their immune status and the interactions between the two.
Since vaccines became widespread, none of the SARS-CoV-2 variants has proven to be more serious than the previous one.
There has not been any that has escaped the immune system in such a way that it produces a greater proportion of deaths or hospitalizations in a population with more defenses generated both by injections and naturally thanks to infections.
And for the moment, XBB.1.5 does not seem to be an exception.
When a variant causes a huge number of infections, however, it also statistically increases the number of people who become seriously ill or die, even if it is much less deadly than the previous ones.
Even so, since vaccination began, the waves have caused fewer and fewer hospitalizations in Spain.
This confirms that the variants are getting milder: even with millions of infections (some studies estimate more than 12 million in Spain in the seventh wave alone) they are not capable of stressing the capacity of the Intensive Care Units , although they do cause the death of hundreds of people, especially the very old and vulnerable who suffered from other diseases and who the covid manages to decompensate definitively.
For this reason, the health authorities urge those over 60 years of age to get the second booster dose, which is more effective than the previous ones to protect against omicron variants.
In Spain, vaccination figures have been stagnant for weeks: just over half of the elderly population has received it.
For technical reasons, the omicron has been the last officially baptized with a Greek letter so far.
All the rest have been sublineages that responded only to letters and numbers and that have sometimes received improvised nicknames to be identified, with names such as "centaur", "hound of hell" or "nightmare", which was the first nickname that spread for the XBB variant.
"Kraken", which refers to a sea monster from Scandinavian mythology, was the brainchild of Ryan Gregory, a biology professor at the University of Guelph (Ontario, Canada), who tries to make information about new technologies more accessible. variants.
Hence substitute a number for a name like this.
It happens, however, that normally these new bloodlines named in a conspicuous way are neither as hellish nor as nightmares nor as monstrous as their name suggests.
Of the hundreds of variants that have circulated and the dozens that have been identified as a danger, only a few have managed to prevail, and in an increasingly less virulent way.
The WHO warns that the more infections occur, the more likely the virus is to mutate and escape the immune system.
It is an inherent risk of any virus: that at some point it becomes more deadly, as happens with the flu, which has repeatedly caused serious epidemics throughout history.