The question that this project seeks to answer, is whether mobile phones can be used to increase the measles vaccination coverage and timeliness in Guinea-Bissau. The intervention will be evaluated in terms of direct health outcomes and cost/benefit analysis, generating evidence that could help policy makers making informed decisions about implementing mHealth interventions at a national level.

The intervention takes the form of a randomized controlled trial in which text messages (SMS) as well as voice calls are scheduled and delivered to mo thers to remind and encourage them to have their children timely vaccinated against measles. In addition, the messages will include relevant information about opening hours and availability of the measles vaccine at the mothers' local health facilities thus improving coordination. The trial will include three different randomization groups with approx. 350 participants in each group. The first group will receive SMS messages, the second group will receive a voice call in addition to the SMS messages, and the third group is a control group that does not receive any intervention.

Study participants will be enrolled following birth at one of three health centers in different rural regions of Guinea-Bissau. Before the measles vaccine is scheduled to be given, at 9 months of age, mothers will receive the intervention message depending on their assigned randomization group. When the measles vaccine is administered, the child will be registered as having received the measles vaccination.

A follow-up phone interview will be conducted at 12 months of age for all children participating regardless of randomization group and whether or not they received the measles vaccine. All participating children, who at that time still have not received the measles vaccine, will be offered the vaccine at the expense of the project.

Inclusion Criteria:

• the mother has access to a cell phone (either her own phone or the phone of a household member)
• the mother lives in the uptake area of the health center.

Exclusion Criteria:

• the mother does not have access to a mobile phone.