Two people in China who received swine flu vaccinations died in the past week but at least one death appears unrelated to the vaccine and the other was being investigated.
The country's health ministry reported the deaths late Friday on its Web site _ the first time China has announced deaths with potential links to the Chinese-made swine flu vaccine.
An autopsy showed one victim suffered a heart attack and, "experts have basically ruled out the possibility that the patient's sudden death was the result of immediate allergic reactions to the flu vaccines," the ministry statement said.
Experts were waiting for more lab results, it added.
An autopsy on the second person was scheduled for late Friday, but no results had been reported Saturday morning.
The statement gave no details on the two people, and phone calls to China's health ministry went unanswered Saturday.
The Hunan provincial health department in southern China posted a statement on its Web site Friday saying a teacher died Monday while playing basketball, eight hours after being vaccinated.
A spokeswoman for the World Health Organization office in China said the second death was a man from Tianjin, southeast of Beijing.
"Our assessment of the safety of the Chinese vaccine hasn't changed," said spokeswoman Vivian Tan. "The deaths are unfortunate, but we need to get to the bottom of it."
The health ministry has said more than 13 million Chinese have received the swine flu vaccine.
"So far from the sheer numbers vaccinated, there's a very small number of mild and ever smaller number of serious reactions. We still believe it is generally safe and effective," Tan said.
The health ministry statement said 1,235 people had been suspected of having abnormal reactions to the vaccine as of Wednesday. Reactions included fever and swelling.
Fifteen people had relatively serious responses such as anaphylactic shock, a severe allergic reaction that can be deadly.
The health ministry statement said the vaccines are generally safe and vaccinations will continue.
As of Friday, China reported about 66,000 cases of swine flu, including 43 deaths.