About 300 people had received inoculations against measles in the village of Nachodokopele during a recent four-day vaccination campaign. The village is in Namorunyang state, which borders Ethiopia and is part of South Sudan's Equatoria region.
Evidence gathered by the investigators indicates that vaccination team members, who were neither qualified nor properly trained, did not adhere to immunization safety standards approved by the WHO.
A single syringe was reused during the campaign instead of being discarded after a single use. The investigators say that reuse caused a syringe to become contaminated, and this contaminated the measles vaccine vials, which then infected the children.
Measles is a highly contagious, serious disease caused by a virus, yet a safe and cost-effective vaccine is available.
"Measles vaccine is supplied as a freeze-dried product. It's like a powder in a vial," said Dr. William Schaffner, an infectious disease specialist and professor of preventive medicine at Vanderbilt University. This powder must be mixed with an approved diluent -- or diluting liquid -- that comes in another vial, and once combined, "you have an active vaccine that can be used."
The process requires "good aseptic technique," an approved health care method to prevent contamination, said Schaffner, who is also a spokesman for the Infectious Diseases Society of America. Aseptic technique would include not reusing a syringe.
The vaccination team also failed to follow temperature range recommendations to preserve the quality of the inoculations. Instead, they stored the vaccines in facilities that lacked proper temperature control for four days, the investigation found.
"The measles vaccine is a live virus vaccine," Schaffner said, which has been weakened, so it provides protection without making people sick.
"It's also heat-sensitive, so if you reconstitute it and then leave it around -- lying around in hot temperatures -- if you delay administering it, then the vaccine's effectiveness diminishes," he said.
If you somehow contaminate the vaccine, an improper temperature "gives an opportunity for the bad germs that have been introduced into the vaccine to multiply. It's like putting them into an incubator. So then the bad germs can actually grow up, and then when you do administer the vaccine, you're administering a much larger dose of the germ itself."
This is much more likely to lead to a serious infection, such as sepsis.
The South Sudan Ministry of Health has commissioned an administrative committee to review the report and offer suggestions for actions to improve vaccine delivery going forward, according to the WHO.
The Ministry of Health could not be reached for comment for this report.
Struggles in South Sudan
A country in east-central Africa, South Sudan borders Sudan, Ethiopia, Kenya, Uganda, Democratic Republic of the Congo and the Central African Republic. In 2011, South Sudan gained its independence from Sudan
, yet it has struggled with governance, according to the CIA World Factbook. Though a peace agreement was signed by warring parties in 2015, fighting broke out between the two principal parties that signed the agreement, and the country re-entered conflict in July.
As of July, the total population of South Sudan was 12.5 million. In February, the UN announced a formal declaration of famine in parts of Unity state, where 4.9 million are in need of help.
Risk of measles and other preventable diseases is extremely high in South Sudan due to a backlog of unvaccinated children in areas of insecurity. The country has experienced significant measles outbreaks.
"In 2013, there were 145,700 measles deaths globally," the WHO said. "In refugee settings, the death rate from measles may be as high as 30%."
Worldwide, more than 2 billion children have been protected against measles by the vaccine.
"The vaccine is extraordinarily effective in preventing these infections. We'd like to give it to every child in the world," Schaffner said. In use since the late 1960s, the vaccine offers children lifelong protection against the measles virus.
"It's likely there were a whole series of errors in the administration of the vaccine (in Nachodokopele) for something this tragic to occur," he said. "It's, fortunately, enormously rare."