International health experts launched an investigation Thursday into why two Samoan infants died shortly after receiving childhood vaccination injections in a tragedy that has rocked the close-knit Pacific nation.
The tiny country has suspended its vaccination programme and seized all doses for testing after the deaths at the Safotu District Hospital last Friday.
The health department said two one-year-old babies, a boy and a girl, died soon after being administered a vaccine for measles, mumps and rubella (MMR).
A World Health Organisation expert has arrived to investigate and a specialist from UNICEF was also en route, along with a forensic pathologist to carry out autopsies, it added.
"We will investigate the cause and will take the appropriate actions to ensure that the lives of Samoan children will not be compromised in the future," the director-general of health Take Naseri said.
Samoa Prime Minister Tuilaepa Sailele Malielegaoi expressed his condolences at the deaths, which have rattled the nation of 195,000 people.
Malielegaoi, who almost lost his grandson several years ago under similar circumstances, said an inquiry would look at whether negligence was a factor.
Medical experts say the cause of the deaths remains unknown and have warned the tragedy should not be exploited by anti-vaccination activists.
"The message is -- please understand vaccination is very safe, it's very appropriate and everyone should still continue with their appointments as currently planned," Australian Medical Association president Tony Bartone told Sky News.
University of Auckland vaccinologist Helen Petousis-Harris said almost every child in the world received an MMR vaccine or a similar jab and deaths were extremely rare.
"There are two main reasons why something like this might happen," she said.
"Medical error, where the vaccine is prepared for injection incorrectly and the wrong substance is injected, (or) contamination of the vaccine due to leaving it at room temperature for a long period of time."
WHO data shows measles kills about 134,000 children a year and rubella causes some 100,000 children to be born with birth defects such as deafness.
Concerns about the MMR vaccine surfaced in 1998 when a British study, since discredited, linked it with autism.
While the study was found to be a fraud and the autism link debunked, vaccination rates have dropped in some countries as parents prevent children receiving their shots.