South China Morning Post A young Hongkonger who returned from the United States caused a stir earlier this month when he not only tested positive for Covid-19, but was also found to be highly infectious. What made the case unusual was that the 27-year-old man was fully vaccinated in Hong Kong before his two-week trip to the US. But medical experts insist there is no cause for alarm, with Professor David Hui Shu-cheong of Chinese University saying it was thanks to Hong Kong's tough quarantine and contact-tracing regime that there had been no outbreak so far from the case. Experts said the man's increased infectiousness was due to the fast-spreading, highly transmissible Delta variant of the coronavirus, and emphasised that vaccines helped mainly to protect against severe illness and death.