TOKYO • Japan's Health Ministry retrospectively confirmed its first detected cases of the Mu variant of the coronavirus in two people arriving from abroad at quarantine stations in different Tokyo airports.
The Health Ministry announced on Wednesday that the Mu variant was detected in a woman in her 40s who arrived at Narita Airport on June 26 from the United Arab Emirates. The other was a woman in her 50s who arrived at Haneda Airport on July 5 from Britain. Both women were asymptomatic upon arrival.
All travellers to Japan are required to take a polymerase chain reaction test upon arrival and made to wait for their results at the airport. If they test positive, they may be quarantined in a designated facility or hospitalised depending on their symptoms.
Should they test negative, a 14-day quarantine at a residence or a designated facility, depending on the country they travelled from, would be mandated.
Japanese media said the ministry assured people that it would continue to take measures to prevent the spread of the variant by closely monitoring the situation in other countries.
On Monday, the World Health Organisation (WHO) designated the Mu variant, known as B1621, as a variant of interest, the second-highest level in its classification.
It remains unclear how transmissible the Mu variant is or whether it is resistant to vaccines.
In a statement released on Tuesday, the WHO warned that the variant "has a constellation of mutations that indicate potential properties of immune escape", meaning that it contains mutations that could reduce the efficacy of inoculations against Covid-19.
The WHO also said that preliminary data showed vaccines were less effective against Mu, in a vein similar to that for the Beta variant discovered in South Africa, and is considered to be more contagious than the original coronavirus.
At present, the WHO classifies the Alpha, Beta, Gamma and Delta strains as variants of concern.
The Mu strain was first detected in Colombia in January but has since been confirmed in at least 40 countries.
Currently, the Delta strain, which originated in India, is the most prevalent variant in Japan, accounting for around 90 per cent of new infections in the country.
