Japan announced the detection of the new variant on Sunday, but officials have emphasised that there is no evidence yet that it is any more transmissible or dangerous than others.
"In order to further analyse the variant, we need to isolate it first," a health ministry official explained.
"It's hard to say right now when we will be able to release the details," he said, adding the process could take weeks or months.
The variant was found in two adults and two children who arrived in Japan on 2 January from Brazil.
The health ministry said one of the four, a man in his forties, has been hospitalised with breathing difficulties, while a woman and male child developed mild symptoms and a female child was asymptomatic.
WHO notified by Japan
The World Health Organisation said Monday it has been notified by Japan about the new variant, warning "the more the virus spreads, the higher the chance of new changes to the virus."
Viruses mutate regularly, and not all mutations make the disease easier to catch or more serious.
But the discovery of a coronavirus variant in the UK that is significantly more transmissible, and a second strain in South Africa, has raised concerns about whether a vaccine-resistant version could eventually develop.
Japan's National Institute of Infectious Diseases has said there are some similarities between the newly detected strain and the ones found in the UK and South Africa.
