There are signs that the “stealth” omicron subvariant, called BA.2, is gradually spreading in Japan and experts worry that it could prolong the sixth wave of infections or drive another surge of cases later this year.

The other omicron sublineage, BA.1, currently accounts for more than 90% of all infections in Japan and overseas. But the new BA. 2 subvariant, which differs in the spike protein and is said to be substantially more infectious than BA.1, is fast replacing BA.1 in some countries. And with signs that the community transmission of BA.1 has already begun, Japan could be next.

So will Japan need to brace for a further strain on the health care system and a surge of cases and deaths? Below, we examine the two known types of the omicron variant and what BA.2's spread could mean for the nation's health care system.