Saada, head of education at the Djiboutian health ministry, explained: "This is different from the two other [previous] campaigns. The goal is to reach more households, farther away, hence the bus."
As part of a national health team that conducted the campaign, she joined colleagues to vaccinate children against poliomyelitis (polio), measles, whooping cough, diphtheria and tetanus - five major diseases that remain potential threats to children under five years old in the Horn of Africa country.
The exercise was organised by the Djibouti ministry of public health with the United Nations Children's Fund (UNICEF), World Health Organization (WHO), USAID and other partners.
Despite ongoing efforts, said Salah Mohammed, head of the vaccination programme at the health ministry, the threat of disease from neighbouring countries remained - especially Somalia and Yemen, which face the risk of polio.
"Somalia and Yemen registered the reappearance of poliomyelitis and at this moment many Djibouti families flee the scorching heat to head to these countries for the holidays," Salah said. "This vaccination campaign is taking place at the right time and will help prevent contamination of people going on leave."
At Einquilla health centre in Djibouti City, however, some mothers said they would have their children vaccinated at health centres and not in bus caravans. Kadra Osman, a 23-year-old mother, who had brought her nine-month-old daughter, Isir Ali, said: "Even during the other vaccination campaigns, I brought my daughter to the centre; it is more reassuring."
Fatouma Ahmed, 31, who had brought her two-year-old son, said she was scared of the bus campaign. "When we were young, the vaccination campaign was carried out once a year. Now, it is more than three times a year. I fear that these vaccines will make us sick."
The buses, however, rumbled on. Kadidja Djama, a 21-year-old nurse who was riding in one of the buses in Djibouti, said: "It is a short and easy campaign; we will stay near the bus where we have installed our equipment. During the other campaigns, we were the ones moving with our thermos from door to door. It was not easy under this sun and with this heat."
The campaign is part of a five-year strategy to improve vaccination coverage against diseases such as polio across the country. Last year's coverage, according to Abdallah Abdilahi Miguil, Djibouti health minister, rose to more than 80 percent although the threat of polio remained serious, especially after cases were reported in neighbouring Somalia.
The polio virus enters the body orally and infects the intestinal lining. It may enter the bloodstream and the central nervous system, causing muscle weakness and often paralysis.
Last year, the UN-backed Global Polio Eradication Initiative launched a campaign to vaccinate more than 34 million children in the Horn of Africa against the virus, covering Djibouti, Eritrea, Ethiopia, Somalia, Sudan, Yemen, parts of Kenya and the Democratic Republic of Congo.
Djibouti has undertaken vaccination initiatives against polio since 1988 and its last reported case of polio was in 1999. Despite logistical constraints, its polio eradication campaign is considered a success, with up to 95 percent of all children in Djibouti City vaccinated.
The five-year programme includes the introduction of vaccines against hepatitis and meningitis, and mandatory health cards for school-going children to show that the child had been vaccinated.