The two nurses implicated in the tragedy, Luse Emo Tauvale and Leutogi Te'o, pled guilty to manslaughter last week and will be sentenced later this month.
The Director General of Health, Leausa Dr Take Naseri, said every vial of the vaccine should be mixed with one vial of dilutant, but the vaccine was mixed with something else.
He said he's worried many parents have stopped taking their children to get any vaccines at all.
RNZI correspondent in Apia, Autagavaia Tipi Autagavaia, says it won't be easy convincing parents the vaccine is safe.
