Kraken, the latest and most virulent strain of Covid, has been detected in Spain after becoming the latest import from the USA.
Known technically as XBB.1.5, Kraken is making its way through the United States and infecting all and sundry, though it does not appear to be more severe.
The World Health Organisation (WHO) has been tracking the XBB variant, a fusion of two Omicron strains, since early December.
Two mutations of this variant have given rise to XBB.1.5, which is quickly becoming the dominant strain globally, particularly in the US, where it accounts for nearly half of all cases.
The WHO has detected the variant in 25 countries, including Spain, where only a few sporadic cases have been identified and it is not yet dominant.
Both random sequenced samples and wastewater analyses conducted by the Ministry of Health have found a clear predominance of BA.4 and BA.5, which have been the dominant strains since last summer.
The nature of the virus means that for a variant to become dominant, it must be more contagious than previous strains – otherwise, it would not spread as widely.
However, the transmission capacity of a virus is dependent on many factors, such as the interaction with its hosts – in this case human beings, their immune status, and the interactions between the host and others.
Since vaccines have been widely distributed, none of the SARS-CoV-2 variants have proven to be more severe than previous ones.
None have escaped the immune system to such an extent as to cause a higher proportion of deaths or hospitalisations in a population with greater defences generated both by injections and naturally through infections.
So far, XBB.1.5 does not appear to be an exception, although when a large number of people get infected, serious illness and death also increases.
Still, since vaccination began, waves in Spain have resulted in fewer and fewer hospitalisations.
This confirms that variants are becoming milder: even with millions of infections (some studies estimate more than 12 million in Spain alone in the seventh wave), each successive wave is not capable of putting a huge strain on intensive care unit capacity.
The good news is that the vaccines currently in use appear to be effective against the Kraken.
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