Photo/Illutration An electron microscope image of COVID-19’s Delta variant (Provided by the National Institute of Infectious Diseases)

The National Institute of Infectious Diseases (NIID) has placed the Omicron variant of the novel coronavirus into the category of “greatest alarm,” prompting the health ministry to issue warnings and instructions to municipalities.

NIID said Nov. 28 that Omicron is now a “variant of concern” (VOC), a category that includes the Delta variant that had spread across Japan and severely strained medical services.

Following the announcement, the Ministry of Health, Labor and Welfare called on municipal governments to ensure that they thoroughly conduct genome analyses on samples that test positive for COVID-19.

Although Japan had no cases of Omicron infections as of Nov. 27, NIID warned that the new variant could be detected in the country in the days ahead.

According to NIID, Omicron contains about 30 mutations to the spike protein, the region that spreads the virus.

The World Health Organization had designated Omicron as a VOC on Nov. 26.

NIID had designated Omicron as a “variant of interest” on Nov. 26, a category just below VOC.

But it upgraded Omicron’s category to the most alarming one for a number of reasons.

One is that Omicron has rapidly overtaken Delta as the most widespread variant in South Africa.

Another reason is that Omicron’s large number of mutations, the most of any variant found so far, has raised the possibility that it could be more adept at eluding the efficacy of vaccines and may increase the risk of reinfection.