The resurgence of the COVID-19 pandemic in Shanghai had already begun in late February before the city’s first case was discovered on March 1, a senior official with the city’s Center for Disease Control and Prevention declared yesterday.

Due to the high-concealing nature of the dominant Omicron variant of the coronavirus, COVID-19 was already being transmitted on a certain scale across the city when the first positive case was detected, Sun Xiaodong, deputy director of the Shanghai CDC, said.

“The virus then spread rapidly across local wholesale markets, wet markets, companies and other gathering places and sites, triggering a wide range of community transmission in a rather short period of time,” he explained at the city’s daily COVID-19 press briefing.

Shanghai reported the first locally transmitted COVID-19 case on March 1. The 56-year-old female retiree, who lives at 155 Zhidan Road in Putuo District, went to Tongji Hospital after getting fever.

Since then, the city’s pandemic saw a “geometric growth” in the early stage and the growth range has since been increasing rapidly, Sun noted.

As of Sunday, the city had reported more than 500,000 COVID-19 cases.

According to gene sequencing done by the center, the local pandemic was mainly caused by the Omicron BA.2 and BA.2.2 subvariants, which are highly contagious and spread fast, Sun revealed.

Due to the short incubation period of about three days on average, the Omicron variant can be transmitted to the third generation within a week.

In Shanghai, the number of cases increased to over 1,000 in half a month in mid-March and then grew by tenfold to over 10,000 within 10 days. It took another 10 days for the infection number to surpass 100,000 in early April.

Furthermore, the transmissibility of Omicron is stronger than influenza and previous coronavirus variants.

Without protection, a positive case can infect 9.5 others. That is the reason for the pandemic surge at some local work places with a large density of people, he pointed out.

The large proportion of asymptomatic cases, accounting for about 90 percent of the total in the city, has made the infections hard to detect. Most of these infections suffer mild symptoms, such as runny nose, sneezing or sore throat, so many of them just treat it as normal cold or flu and don’t go to hospital, Sun added.

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