The timeliness of vaccination refers to a child receiving their vaccination at the recommended time and is calculated by subtracting the date of birth from the vaccination date. Vaccines were administered on time if they were received within the first year of life and within the time limits set by the World Health Organization (WHO) [1].
Vaccination timeliness is defined as administering vaccines at the earliest age possible and adhering to the recommended intervals between doses. The timing of vaccinations is an important mechanism for developing protective antibodies and providing effective disease protection in children. Only when an effective vaccine is administered at the right time will it result in disease protection by strengthening community immunity and preventing the spread of infectious diseases, particularly during illness outbreaks; increased adherence to vaccination timeliness protects children before exposure and lowers morbidity.[2]–[5].
It is crucial, especially for diseases like pertussis and Haemophilus influenzae type B (Hib), which cause the majority of deaths within the first six months of life. Additionally, prompt vaccination protects infants who are too young to receive a full vaccination and maximizes herd immunity [6]. On the other hand, early immunization may not produce an antibody that protects against the diseases [7]. Because vaccinations given too soon or without a suitable time interval between doses, may not be totally protective (lead to a misleading sensation of protection) [8]. Ad also, postponing immunizations raises a person's risk of contracting a potentially fatal VPD [9]. These will lead to lower community-level herd immunity and intervention success rates [10], full vaccination series completion rates [11], and elevated risk of infectious illnesses under control [12].
Globally, immunization is one of the maximum cost-effective techniques in growing infant survival, saving 2–3 million infant deaths every year from vaccine-preventable illnesses (VPDs) [13]. A vaccine can also additionally have avoided one disorder out of each twenty that claimed an infant’s life in 2019 [14]. Even with the excessive vaccination rate of 85% global in 2017, a few children nevertheless experience delays in receiving fundamental vaccinations, especially in low-profits countries [15]. Despite the truth that vaccination timing is an essential public health objective for monitoring vaccine adherence, this information is normally insufficient due to the fact the most extensively utilized metric is vaccination coverage [8].
Timeliness of vaccination is a measure of the quality of vaccination programs, but it has received less attention than other program performance indicators [16]. Therefore, inadequate supply chain management, limited access to health care, and suboptimal performance of service providers are contributing to suboptimal vaccination schedule timeliness in low- and middle-income countries (LMICs) around the world [17]. Additional country-specific studies are also needed to elucidate the impact of schedule completion bottlenecks on dose-specific delays in sub-Saharan African (SSA) countries [18].
Previous literature shows that 87.5% in Ghana, 94% in Israel, 82% in Philadelphia, 64% in Ethiopia, 71% in New Zealand and 87% in Uganda were vaccinated on time[19]–[24]. Previous studies have shown that the timeliness of vaccination is associated with place of delivery, lower education level, antenatal care visits, unplanned pregnancy and male gender of the child, and the oldest age of the mother/caregiver, maternal age, vaccine hesitancy, multipara, residency, and the poorest quintile. However, these variables vary depending on the study setting [5], [17], [25]–[29]. In Ethiopia, vaccinating children at an adequate time interval is the major method in minimizing avoidable childhood mortality from measles, pneumonia, diarrheal illnesses, and other VPDs [30].
In general, advanced countries have given cautious concept to the timing of childhood vaccinations; however, comprehensive research in low-earnings nations—specially Ethiopia—has been few[31]. Untimely vaccinations have significant impact on immune system functioning and are likely to contribute greatly to the preventable disease burden in Ethiopia, allowing for transmission among those in the age group at which they are the most vulnerable to severe disease with tragic consequences [32]. Previously, most studies conducted in Ethiopia assessed complete vaccination coverage and related factors; however, there is limited information about timely vaccination and its influencing factors, illustrating an essential research gap that must be filled. Because of this, full vaccination is most effective in identifying the number of children vaccinated, however it does not provide adequate information about the countrywide vaccination schedule, which is critical for protecting children from vaccine-preventable illnesses if they receive vaccines within the recommended timeframe. In addition, this study included children aged zero-11 months, which was excluded from previous research performed in Ethiopia. In order to help program implementers and frontline health workers recognize vaccination timelines and its related factors to plan for default tracing mechanisms. So, this study aimed to evaluate vaccination timelines and its related factors among children aged zero to 23 months in the study area.