SAN FRANCISCO: Two Covid strains first detected in California have been officially defined by the US Centers for Disease Control and Prevention as "variants of concern". The variants, dubbed B.1.427 and B.1.429, may be about 20 percent more transmissible, the Centers for Disease Control and Prevention (CDC) revealed on Sunday.

Some coronavirus treatments may also be less effective against the strains, it added. The officials noted the California variants inflict "significant impact on neutralisation by some, but not all, Emergency Use Authorisation therapeutics" and has "moderate reduction in neutralisation using convalescent and post-vaccination era", Xinhua news reports.

The "variant of concern" was defined by the CDC as there is evidence of an increase in transmissibility, increased hospitalisations or deaths, a significant reduction in neutralization by antibodies generated during previous infection or vaccination, reduced effectiveness of treatments or vaccines, or diagnostic detection failures.

Viruses constantly change through mutation. As expected, multiple variants of SARS-CoV-2 have been documented in the US and globally throughout the Covid-19 pandemic.

Currently, there are five coronavirus strains classified by the CDC as "variants of concern".

Besides the two detected in California, the other three are B.1.1.7, which was originally found in Britain; B.1.351 discovered in South Africa; and the P.1 strain detected in Brazil. A total of 4,855 cases of coronavirus variants has been reported in the US, according to latest data of the CDC.

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