Kazakhstan has suspended a nationwide measles vaccination campaign for teenagers after more than 100 students fell ill after receiving inoculations.
The Health Ministry says a group of specialists has been set up to inspect the vaccines and a criminal investigation has been launched into claims that doctors and teachers had violated procedure.
The ministry insists that immunizations, which were halted on February 19, will resume on March 2.
The nationwide campaign was launched to immunize, or provide booster shots, to some 900,000 teens aged 15-19.
More than 320 measles cases were recorded in Kazakhstan in 2014, a fourfold increase over the previous year, and the majority were in that age group, according to the Kazakh Health Ministry.
Some parents have expressed anger at the way the compulsory vaccination campaign has been conducted.
"My daughter was vaccinated despite my refusal," says Zhumagul Demeubaeva, a resident from the western city of Zhanaozen. Her teenage daughter, Asem, has been hospitalized in intensive care following a measles inoculation.
"When I told the school I was against her being vaccinated, the head teacher asked me to provide a written notice," says Demeubaeva. "But I didn't have time to write it."
According to Kazakh law, parents can be granted vaccination exemptions for their children but they must submit written requests.
Those who seek exemptions often cite health or religious reasons and suspicion about the contents of vaccines is common.
Sixteen-year-old Gaukhar Karmysova, who fell ill after inoculation, has experienced cramps and breathing difficulty.
The girls' parents, along with 15 other families, filed official complaints, prompting the investigation.
"I demand that the Health Ministry restore my daughter's health," says Karmysova's mother, Zhanar Izbasarova. "What am I going to do if she becomes permanently disabled?"
Doctors say symptoms such as cramps, seizures, and breathing problems are rare side effects of the measles vaccine and occur in only about one of every 1,000 cases.
They say that occurrences of vaccine-related seizures are less frequent than seizures that occur as a direct result of a measles infection.
The children are expected to make full recoveries.
Doctors say teens who fell ill after receiving measles boosters reported a variety of symptoms, including high fevers, numbness in their extremities, pain, and nausea. Almost all the patients fully recovered and were discharged from the hospitals within days.
"Normally, 10 percent of children experience side effects after being vaccinated," says Almabek Bisen, deputy head of the Mangistau region's health department. "In our region, only 0.03 percent of those who received shots have had side effects. There is no reason to worry."
The ministry has sought to reassure the parents about the vaccines being used, noting that they were certified by the World Health Organization (WHO) and are being used in 45 other countries, including in Western European states.
Melity Vujnovich, the head of the WHO office in Kazakhstan, hopes authorities will resume the vaccination campaign.
"In Kazakhstan, the risk of getting infected by measles still exists among children and young adults who have not been vaccinated or not fully vaccinated," she said. "The aim of the campaign is to decrease that risk."
The immunization drive, which began in early February, comes amid a measles outbreak in neighboring Kyrgyzstan, where thousands of cases have been recorded since the start of the year.
Kazakhstan recorded only 12 cases in January, but health officials are determined to eliminate any chance of an outbreak.
In 2014, more than 21,100 people were given booster vaccinations in areas where measles cases were reported.
The Health Ministry said it was a preventative measure to protect those who might have been exposed to the highly contagious disease, which can pass from person to person through fluids spread through the air by coughing and sneezing.
Last year, the authorities also identified and provided first-time vaccinations to more than 86,000 people across the country.
Regular measles inoculations, meanwhile, are being carried out for children aged 1 to 6.
The Health Ministry says the government has purchased an adequate number of vaccines, including 1 million doses for the current campaign, and has distributed them to regional health centers.
The ministry's drug-regulation agency is expected to complete its examination of the vaccines by March 1.