Vaccination, one of the greatest achievements in medicine and public health, has greatly reduced morbidity, mortality, and health care costs [1]. Although many developing countries have seen a major reduction in vaccine-preventable diseases (VPD) owing to sustained use of vaccines, vaccination has not reached its full potential and at least 2 million people die every year from VPD [2]. Therefore, for vaccination programs to be effective, high rates of coverage must be maintained.

The World Health Organization and the United Nations Children’s Fund developed the Global Immunization Vision and Strategy (GIVS) 2006-2015. One of the set goals of GIVS for any country is to reach at least 90% national vaccination coverage and at least 80% vaccination coverage in every district or equivalent administrative unit [3].

In Yemen, the strategy for the national Expanded Program on Immunization (EPI) 2011-2015 was to reach 95% coverage at the national level, and not less than 80% for diphtheria, tetanus, and pertussis at the district level by 2015 [4]. However, a major demographic challenge for reaching this target is a very scattered population, with more than 130,000 population sites all over the country [5]. Although, the political crisis that started in 2011 with the Arab Spring had negatively affected the health system and accessibility to health services, including vaccination, the political situation stabilized after 2012. However, in March 2015, a major war broke out and left only 45% of health facilities functioning. Yemen, which had a fragile health care system before the onset of war, did not have the infrastructure to withstand such a catastrophe and is currently on the brink of collapse. In the past 2 years, continuous war has led to the destruction of health care facilities and has made access to the ones standing difficult for those in need. Before the war, Yemen had a relatively stable vaccination rate reaching 70% to 80% of the target population; however, this dropped remarkably after the war [6,7]. VPD such as measles, cholera, and diphtheria saw a sudden surge after the beginning of the war [7-11]. Polio importation in such a critical situation also remains a major threat not only for Yemen but also for its neighboring countries.

This study aimed to determine the immunization coverage of the children under 1 year, during the 2015 war.

Despite recent progress in vaccination coverage in Yemen, a very scattered population, with more than 130,000 population sites all over the country, poses a major challenge. Furthermore, the current political situation and insecurity have negatively affected the progress. Our findings showed a gradual increase in the coverage of penta-3 vaccine and MCV during 2012-2014, compared with the year 2011 that witnessed the political crises and the Arab Spring. Such an increase might be owing to the relative political stability and improvement of security after the uprising came to a successful conclusion. However, Al Jawf and Sa’dah governorates did not show such an increase as they continue to suffer from insecurity and fights, in addition to having sparse population with difficult access to vaccines and poor community awareness and wrong beliefs regarding immunization [12]. Furthermore, in all these years the coverage was still below the national target [4] and lower than the coverage in the neighboring countries, including Saudi Arabia (96%) and Oman (99%), but better than that in Somalia (65%) [13,14].

The coverage remarkably dropped in 2015 owing to the eruption of the war. Such a drop was more apparent in governorates that witnessed confrontations such as Sa’dah, Lahj, and Taiz. For example, Taiz governorate showed a drop in penta-3 vaccine coverage from (102,455/110,755) 92.51% in 2014 to (83,182/113,535) 73.27% in 2015 and Sa’dah from (17,511/26,779) 65.64% to (13,849/27,754) 49.90%. However, the coverage increased in Ibb and Raymah governorates that were less affected by the war and showed an increase in their population because of displacement from less secure and confrontation-prone governorates. For example, Raymah showed an increase in penta-3 vaccine coverage from (15,868/18,255) 86.92% to (19,871/18,810) 105.64% and Ibb from (93,106/99,919) 93.18% to (103,435/102,417) 100.99% in 2015.

In conclusion, this analysis shows the marked negative impact of the 2015 war on immunization coverage, especially in the governorates that witnessed armed confrontations. This could put Yemen at more risk of VPD outbreaks and polio importation. Besides the ongoing efforts to stop the Yemeni war, strategies for more innovative vaccine delivery/provision and fulfilling the increasing demands are needed, especially in governorates with confrontations. Enhancing EPI performance through supportable investments in infrastructure that was destroyed by the war and providing decentralized funds are a prerequisite. Further studies to assess the effect of continuous war on vaccination coverage and to measure the resilience are recommended.