Explainer | Coronavirus: should Hong Kong be concerned about global rise in BA.4 and BA.5 cases? Here’s what we know about more transmissive Omicron subvariants

Omicron subvariants BA.4 and BA.5 have triggered widespread outbreaks around the world in countries such as the United States, South Africa and the United Kingdom, leading to concerns that the more transmissive strains could also affect Hong Kong, which has just recovered from a fifth wave of infections and is about to negotiate reopening the border with mainland China.

Here is what we know about the subvariants so far.

1. Why have subvariants become a concern in Hong Kong?

Since the city began easing social-distancing curbs in May, there has been a rebound in Covid-19 infections, with the numbers rising to more than 1,000 in mid-June, while relaxed restrictions for overseas arrivals has led to an increase in imported cases. The number of local infections passed 3,000 a day on Thursday before dropping a little on Friday.

While Omicron subvariant BA.2 remains the dominant strain in the city, other ones, which are widespread overseas, have found their way into the community. Health authorities have reported dozens of cases per day involving subvariants BA.2.12.1, BA.4 and BA.5.

According to ​​science journal Nature, the three lineages carry mutations that allow immune escape, meaning they can evade protection offered by vaccines and previous infections.