It was due to have ended on December 15.
Prime Minister Tuilaepa Sailele Malielegaoi said it had been extended so as to administer vaccinations to the remaining population who have yet to be immunised.
This is an estimated 16,000 people among the population of approximately 190,000.
The measles epidemic has killed 72 people in the country since it began two months ago. There have been no fatalities in the last 24 hours.
On Saturday afternoon Samoa's Ministry of Health confirmed a total of 5,154 measles cases since the outbreak started.
There were 74 recorded in the last 24 hours.
There are currently 160 measles cases who have been admitted to a health-care facility, 16 of them are critically ill children.
Meanwhile New Zealand will contribute $NZ1 million to an international fund to tackle measles in the Pacific, Foreign Minister Winston Peters said.
Peters announced the funding for the joint United Nations Fund for Children (UNICEF) and World Health Organisation (WHO) Pacific Regional Action Plan for Measles.
He said vaccination was the most effective way of avoiding illness and a costly health emergency.
"This plan offers immediate preventative action. It allows for the flexibility to respond to additional requests from other Pacific nations and offers an efficient way of working regionally," he said.
Peters said the funding would help to identify regions vulnerable to the disease and early interventions to prevent further outbreaks.
Children under five will be targeted for vaccinations, as well as new mothers and their families.