Hong Kong has detected seven cases of a highly infectious Omicron subvariant that has raised alarm overseas, authorities have said, although experts have stressed that the local infections should not be a cause for concern.

The Department of Health said on Monday seven cases of XBB.1.16, known as Arcturus, which was first detected in India earlier this year, were found among the samples collected in the city.

Top health expert Professor David Hui Shu-cheong of Chinese University on Monday said the subvariant was highly transmissive but the number of severe cases had not risen in the regions where it had been found.

“XBB.1.16 was found in a few samples in Hong Kong. I believe it can mostly be found in imported cases, as it was first found in India,” Hui told a radio programme.

“The transmissibility is quite high but the severity has not gone up. In the countries that have reported cases with this subvariant, there has been no increase in patients admitted to intensive care units or deaths … We do not need to be too worried.”

Hui said those who had been vaccinated or infected would be able to produce sufficient T-cell responses to fight the subvariant. T-cells are a type of white blood cell crucial for combating infection.

XBB.1.16, also known as Arcturus, is a subvariant of the Omicron sublineage BA.2. Omicron was responsible for the fifth and most severe wave of coronavirus cases that arose in Hong Kong in the first half of 2022.

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Omicron subvariants such as BA.5 and BA.2.12.1 continued to affect the city throughout the year, but did not lead to a rise in severe cases or deaths as most of the population had either been inoculated or infected.

The World Health Organization said a study had shown Arcturus, which had appeared in 29 countries so far, had a higher growth rate compared with subvariants XBB and XBB.1.5, but their immune evasion characteristics were similar.

India was reported to have experienced a surge in Covid-19 cases from January, which was believed to be caused by Arcturus.

The new subvariant is also gaining traction in the United States. In an update last week, the US Centres for Disease Control and Prevention said that XBB.1.16 accounted for more than 7 per cent of all coronavirus samples it had collected in the country, up from 3.9 per cent in the previous week.

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About 40 per cent of the Covid-19 case samples collected by Hong Kong authorities were linked with various subvariants from the XBB strain, Hui said, but no outbreaks had been reported.

He said a number of children in India who were infected with Arcturus had developed acute infectious conjunctivitis, known as red-eye syndrome.

“[Parents] have to take their children to the doctors if their corneas turn red and begin to tear up. Normally if you rub your eyes, they will recover quickly after turning red. This subvariant will also cause fever with a relatively higher temperature,” he said.

Respiratory medicine expert Dr Leung Chi-chiu also said residents had no cause for concern, adding it was uncertain whether the subvariant would become the dominant strain in Hong Kong.

“Different regions have different experience in the pandemic and vaccination coverage. We have several hundred Covid-19 subvariants. There is a high degree of uncertainty over which subvariant will become the next dominant strain in the city,” Leung said.

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“Even if it becomes the dominant strain, it will not lead to an exponential increase in infections. As we have a high level of herd immunity, other than high-risk groups, most people will not develop serious symptoms after contracting the subvariant.”

He said as the subvariant took about three months to cause cases to surge in India, its transmissibility was far weaker than past strains.

Leung responded to reports of conjunctivitis developing in infected children in India, saying the information was simply anecdotal and lacked concrete figures. He said more data had to be collected outside the country to ascertain whether this was a common occurrence.