The first death from the new Covid strain has been recorded as countries across the globe record more cases.
An unnamed elderly man has died in Thailand, Dr Supakit Sirilak, director-general of the Medical Sciences Department said.
He said that 27 cases had been detected and that the deceased was "an elderly foreigner" with underlying health conditions.
He continued: "His death, therefore, may not directly reflect the severity of this subvariant but rather its impact on other risk factors."
Arcturus, which is a subvariant of Omicron, was first seen in India and has been on the World Health Organisation's watchlist since the end of March.
Prof Dr Yong Poovorawan, who heads the Centre of Excellence in Clinical Virology at Chulalongkorn University’s Faculty of Medicine, said to PBS it will inevitably become Thailand’s dominant subvariant soon.
Between April 9 and 15, the number of patients hospitalised with the virus was up two and a half times from the previous week in Thailand.
The subvariant is skyrocketing infections in India and has prompted health officials to reintroduce mandatory mask-wearing among other measures.
Russian health watchdog Rospotrebnadzor announced on Tuesday that it detected its first of several cases and said it may have "greater contagiousness."
Rospotrebnadzor's statement continued: "But is not characterised by high pathogenicity. That is, the disease caused by it proceeds in a mild form."
The Centres for Disease Control and Prevention (in the US), said Arcturus is causing 7% of coronavirus cases in the country. Meaning it is now in second place behind its cousin Omicron.
Indonesia has reported five new cases of Arcturus subvariant.
The new variant is reportedly 1.2 times more infectious than the Omicron variant, according to a study by the University of Tokyo published on the biology research website bioRxiv.
Dr Vipin Vashishtha, the former head of the Indian Academy of Pediatrics Committee on Immunisation, tweeted that pediatric cases of Covid were on the increase for the first time in six months.
Conjunctivitis - an eye infection causing redness, itchiness and swelling in the eyes - has also been present in paediatric cases.
Mayo Clinic viral disease expert Matthew Binnicker, PhD, told The Seattle Times: "One new feature of cases caused by this variant is that it seems to be causing conjunctivitis, or red and itchy eyes, in young patients.
"This is not something that we've seen with prior strains of the virus."
"The emergence of this new variant clearly shows us that the biology of the virus is alive and well and kicking", Dr Bharat Pankhania, a senior clinical lecturer in communicable diseases at the University of Exeter told the Mirror.
