budget – Why is air travel to China currently 4x the usual price?

For the past 15 years, round-trip economy flights from San Fransisco to Shanghai have been close to $1000-1500 per person. Currently the summer prices are between $3500 and $4500 per person. Looking at other destinations, I have not noticed any other region in the world having such a tremendous spike in the prices, but instead, average prices to other destinations around the world (e.g. Europe, the Middle East, Africa) seems lower than before, probably related to COVID-19. What explains why China’s flights are currently ~4 times higher than usual?