Why do we need so many PCR tests? Top expert explains

Imaginechina

Repeated citywide PCR tests are necessary to end the current resurgence 0f COVID-19 pandemic as soon as possible, said Wu Zunyou, chief epidemiologist with China CDC.

Wu made the comments on his Weibo account as the pandemic is in full swing in Shanghai with more than 24,000 cases reported today. Citywide PCR tests have been carried out repeatedly over the past few days.

Wu attributed the increasing number of cases in Shanghai to massive PCR screenings among its residents within a short period of time which uncovered a large number of infected people who had not been identified earlier.

Now that the virus has widely spread among local communities, Wu said the most effective strategy to halt community transmission is to carry out across-the-board PCR tests as quickly as possible.

Since the average incubation period for the Omicron variant is three days, and patients usually start to shed the virus one or two days before their first symptoms, an infected person might not test positive in the first two days.

"The first test helps screen only people who have already started to shed the virus, while those who are infected but test negative would become infective if not identified immediately on the second and third tests," Wu said.

If one tests negative, which means that no virus is detected in his throat, then he's hardly infectious to others in the next 24 hours by breathing or talking, he added.

For a megacity like Shanghai which has a population of more than 25 million, it could take three to four across-the-board PCR tests to finally terminate community spread of the virus, Wu said.

"If a round of tests takes two to three days, then theoretically the goal can be achieved in 10 to 14 days," he said.