>...despite Beijing's loosening of Covid restrictions at the beginning of the month

A possible reason: "China Covid: experts estimate 9,000 deaths a day" https://www.theguardian.com/world/2022/dec/30/china-covid-experts-estimate-9000-deaths-a-day-as-us-says-it-may-sample-wastewater-from-planes

>UK-based health data firm Airfinity said about 9,000 people in China were probably dying each day from Covid, nearly doubling its estimate from a week ago.
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>Cumulative deaths in China since 1 December likely reached 100,000, with infections totalling 18.6m, Airfinity said in a statement on Thursday. It used modelling based on data from Chinese provinces before the recent changes to reporting cases were implemented, it said.
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>Airfinity expects deaths to peak on 23 January with about 25,000 a day, with cumulative deaths reaching 584,000 since December. Since 7 December, when China made its abrupt policy U-turn, authorities have officially reported just 10 Covid deaths.

Due to the fear of new variants coming from China to other countries (only the same variants are being found so far), the US is considering testing aircraft wastewater:

>The United States is considering sampling wastewater taken from international aircraft to track any emerging new Covid-19 variants as infections surge in China.
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>Airplane wastewater analysis is among several options the Centers for Disease Control and Prevention is considering to help slow the introduction of new variants into the US from other countries, a spokesperson for the agency, Kristen Nordlund, said.