Officials of east China's Shanghai Municipality said recently the latest round of COVID-19 outbreak in Shanghai has been one of the hardest challenges in almost two years. But the city still enforces flexible prevention strategies to tackle the challenge.

Starting Wednesday, Shanghai started to use the so-called dynamic COVID-19 screenings. Not all the communities city-wide are under lockdown for screenings, but rather, one batch followed by another. And communities that need to take such screenings are judged by the health commission on their risk levels.

After two rounds of tests done in 48 hours show negative results, lockdown of the residential compound will be lifted.

Wu Jinglei, director of Shanghai Health Commission, said such policies have helped the city to find out many positive cases. More than 50 COVID-19 cases and over 200 asymptomatic infections were reported on Thursday, just one day after the city enforced the dynamic COVID-19 screenings.

"This round of screenings has shown that COVID-19 cases have gathered regionally. We also found some hidden infections and transmissions. These have shown that our screenings are rapid, crucial and urgent, which laid a good foundation for us to cut the transmission chain," said Wu.

So far, some residential compounds have re-opened and people are free to go out. Some are still waiting, as COVID-19 cases have been reported there. Residents will usually get a lockdown notice in advance to allow them prepare food and daily necessities. They can also order food delivery and pick them at the compound entrance.

The Shanghai health commission said virus prevention measures and lockdowns will vary, depending on the risk levels in different regions.

Starting March 18, the city will provide one round of free nucleic acid test for all residents in areas with lower risks. But officials have reiterated that residential communities there will not be locked down.

So far, schools in town have closed and shopping malls have shortened their operation hours. People need to show negative PCR tests results done within 48 hours if they want to arrive into or leave Shanghai.