“As we expedite development of an Omicron vaccine, we consistently make safety and efficacy our No. 1 priority,” Zheng Zhongwei, an official who oversees COVID vaccine development at the National Health Commission, said during a media briefing on Saturday.

On Saturday, officials reported China’s first COVID deaths in two years after two people—one unvaccinated, and both with underlying medical conditions—died. China has recorded over 20,000 new COVID cases this month and placed tens of millions of people in lockdown to curb the spread of the highly virulent Omicron strain.

Data shows China’s domestic vaccines, one produced by Sinopharm and another by Sinovac Biotech, are both highly effective at preventing severe infection and death caused by COVID, but are still less effective than mRNA vaccines.

The recent Omicron outbreak in Hong Kong—where residents have access to both the mRNA-based Comirnaty and the inactivated CoronaVac vaccine—could provide a test case for relative efficacy of each type of vaccine against Omicron.

During its current Omicron outbreak, the death rate for COVID cases in Hong Kong has surged to the highest in the world, principally due to the large number of unvaccinated elderly residents. But the government has mostly withheld data on vaccine fatality rates.

On Sunday, Hong Kong newspaper Ming Pao reported that 87% of the vaccinated who died in Hong Kong had been vaccinated with CoronaVac, suggesting that BioNTech’s mRNA vaccine guarded against death far better than its inactivated rival.

Yet Hong Kong’s local government was quick to rebuff the report, questioning the veracity of Ming Pao’s data and calling the paper’s analysis “misleading.”

“The analysis of vaccine type received by fatal cases is relatively complicated, and investigation on the particular situation, such as age and history of chronic disease of each fatal case, is needed,” the government said in a press release.

The government also noted that the fact “more elderly people [received] CoronaVac vaccine should also be taken into consideration” when comparing apparent efficacy.

According to the government, patients over 80 years old account for 70% of all of Hong Kong’s COVID-related deaths this year. Of those, roughly 74% were unvaccinated, leading to a post-infection “fatality rate” of around 15% for the unvaccinated.

For vaccinated patients over 80, the fatality rate was 5.83% for those who received one dose of CoronaVac, and 3.44% for those who received one dose of Comirnaty. After two doses, the fatality rate dropped to 2.95% for CoronaVac and 1.51% for Comirnaty.

“Both COVID-19 vaccines available in Hong Kong are safe and highly effective in protecting against severe disease and death from COVID-19 infection,” the government said.