Apia, SAMOA — Samoa's health system has better monitoring systems in place following the deaths of two infants last year, the country's nurses' association says.

The two one-year-old babies died after receiving doses of the Measles, Mumps and Rubella (MMR) vaccine which were incorrectly mixed with an expired anaesthetic.

The deaths prompted Samoa to suspend all vaccination for three months and damaged public trust in vaccines across the region, including New Zealand.

On Friday, two nurses who administered the vaccine were jailed for 5 years. Lana Samuelu and Lameko Sui had pled guilty to negligence causing the manslaughter of the infants.

The women, who appeared tearful during sentencing in Samoa's Supreme Court, had hoped for a lighter sentence after prosecutors only asked for just 2 years imprisonment.

But the high-profile case has been swept up in a national response to the incident, which involved the re-training of all nurses. President of the Samoa Nurses' Association, Solialofi Papali'i, said recent efforts had improved health systems, especially involving the storage of medicines at hospitals.

"The nurses follow the rules and check and double check," she said.

More reforms may follow, as Samoa grapples to understand how the deaths happened, even as the two nurses sit behind bars.

On Friday, the country's district court launched a coronial inquest into the deaths, on top of a commission of inquiry which had been pending the nurses' trial.

Still, Helen Petousis-Harris, a vaccinologist at Auckland University, said the jailing of the nurses had "unfortunately" singled them out, letting slide more systemic issues within Samoa's hospitals.

For example, she said, the expired anaesthetic which caused the deaths was stored in the same place as the MMR vaccine.

"That's just one example of creating an environment where something could go terribly wrong. It's an absolute no-no."

Dr Petousis-Harris said Samoa's government had also failed to reassure people that it was not the vaccine but human error which killed the babies.

As news spread of the babies' deaths, conspiracy theories claiming vaccines were unsafe quickly spread on social media.

The government recalled its MMR vaccines as confidence in Samoa's health system plunged, spreading throughout the region.

The Cook Islands also briefly suspended its MMR vaccine programme over the deaths.

And the effects are still being felt. As recently as June, doctors in New Zealand battling a measles outbreak struggled to convince Pacific communities that vaccines were safe.

New Zealand's government - which has been concerned about a growing regional threat cause by weakened health systems - this year stepped in to assist Samoa.

Eight doctors from a district health board in New Zealand travelled to Samoa in June, training nurses at 8 hospitals on Upolu and Savai'i.

Elizabeth Powell, a general manager at Counties Manukau Health, said the training went smoothly and trust among the public in Samoa is improving.

"Samoa [was] able to get a lot of the vaccinations done for their children" during the 10-day trip, she said.