(Bloomberg) -- Beijing reported two more Covid deaths on Sunday as cases spiked, heightening concern the capital could see a return of tougher restrictions. 

The city reported 951 cases for Sunday, the most since Bloomberg started tracking the data on Sept. 1, 2021. A 91-year-old woman and 88-year-old man died yesterday, following the death of an 87-year-old man Saturday. He was the nation’s first documented virus-related death since May 26, when Shanghai authorities reported one fatality. 

The deaths could test the tolerance of Chinese authorities, who earlier this month eased some curbs in a move many took as a sign of a shift away from its strict zero-tolerance policy. After being largely isolated from the rest of the world for the past three years, China shortened quarantine times for inbound travelers and close contacts, and ended a system that suspended international flights tied to too many infected passengers. 

In a potential sign officials are reverting to tighter Covid Zero curbs as cases multiply, Shijiazhuang, a city of about 11 million people near Beijing, has suspended schools, locked down universities and asked residents to stay at home for five days, according to the statement carried by official Shijiazhuang Daily. 

A mass Covid testing exercise will be undertaken in six major districts, and universities will be put into so-called closed loops, where students are unable to leave campuses. All in-person classes at primary and middle schools have been halted.

Read more: Strict Covid Zero Curbs Return to City Rumored to Be Reopening

As Beijing’s cases rise, schools in several districts of the capital have told parents they’re moving to online learning from Monday until further notice. There has been no official confirmation of any district- or city-wide school closures. Some shopping malls in Beijing, including Joy City in the Chaoyang district -- the epicenter of the latest outbreak -- have shuttered all businesses except food take-away services from Sunday, local media reported.

Low vaccination rates among elderly and vulnerable citizens remain one of the biggest hurdles for the country’s full reopening. Only 66% of those aged 80 and above are fully vaccinated and only 40% have gotten a booster. That compares with a vaccination rate of more than 90% for seniors in the US. 

--With assistance from Li Liu.

©2022 Bloomberg L.P.