A vaccination against Japanese encephalitis has left Qiang Qiang, a healthy boy four years ago, into an epileptic who has trouble keeping up at school now.
The seven-year-old is one of dozens of youngsters in the northern Chinese province of Shanxi whose parents believe their children may have suffered serious side effects from vaccines in the country's latest public health scare.
"His teacher at school tells us he is dumb, that he has short memory and cannot follow classes," his father Gao Changhong told AFP.
"We have spent nearly 60,000 yuan ($8,800) to try to cure him, and we really hope the government will take this situation seriously."
A Chinese state media report last month said four children had died and more than 70 others in Shanxi fell ill after they received shots against illnesses such as hepatitis B and rabies between 2006 and 2008.
The China Economic Times report blamed vaccines that had been exposed to excessive heat and should have been destroyed.
The report quoted Chen Tao'an, a whistleblower at Shanxi's Centre for Disease Control (CDC) where the vaccines were being handled, as a key source.
China's health ministry initially investigated reports of bad vaccines in Shanxi in 2008 and found no problems.
But a probe of the latest allegations indicated issues with "management" of the vaccines, though the shots themselves were not faulty when first produced, the health ministry said Tuesday.
It however insisted that the vaccines were not responsible for the four deaths.
According to the World Health Organisation, vaccines that are exposed to high temperatures can lose their effectiveness and trigger reactions.
Shanxi's CDC admitted in a press briefing in March that its former director had been dismissed following irregularities in his ties with the vaccine firm at the heart of the scandal. But it has insisted its shots were safe.
The allegations have triggered yet another health scare in a nation regularly plagued by food and medicine-related product safety concerns.
In the past few weeks alone, authorities have ordered inspections of cooking oil nationwide after reports said up to one-tenth of China's supplies contained cancer-causing agents.
Peddlers in the central province of Hunan have also reportedly been found soaking dry soybeans in green dye and selling them as fresh green beans.
And according to state media, a drug firm in the eastern province of Jiangsu has been accused of using an additive in a rabies vaccine that allowed it to meet inspection standards at a lower cost but compromised its potency.
The State Food and Drug Administration has admitted that "inferior materials" were used in producing the rabies vaccines. It said the firm had been ordered to halt production and some employees were suspected of criminal activity.
The parents of the children in the Shanxi case are convinced their children were harmed by faulty shots.
Wang Mingliang lost his baby son after he received a vaccine against hepatitis B. Xiao'er soon began suffering from spasms and breathing difficulties -- he died months later.
"We spent more than seven months trying to get him well, from Western medicine to traditional Chinese medicine, and none of it worked," he told AFP.
"None of the hospitals we went to managed to find a cause for his illness, and that's when we started suspecting the vaccine."
China has launched a high-profile product-safety blitz in recent years after a string of scares.
But scandals have continued, including revelations that the industrial chemical melamine was added to milk supplies in 2008. At least six babies died and 300,000 were sickened as a result, according to the government.