Peter McIntyre and Tony Walls
From the first vaccine (cowpox, developed by Edward Jenner in 1796), more than 100 years elapsed before additional vaccines for broad population use (diphtheria toxoid, tetanus toxoid, and whole cell pertussis) became available between 1920 and 1940. Then followed inactivated polio vaccine in the 1950s, and live attenuated vaccines for measles, mumps, rubella, and polio in the 1960s. In 1979, global elimination of smallpox was formally certified, with the last human case occurring in Somalia, almost 200 years after Jenner administered cowpox vaccine to James Phipps.
In 2019, global elimination is tantalizingly close for maternal and neonatal tetanus and polio. Despite recent outbreaks, elimination has also been achieved at country and regional levels for measles and rubella and, if achieved globally, will offer, as it has for smallpox, large reductions in child mortality and morbidity and in health system costs. Short of elimination, it is important to define the public health impact of vaccines broadly and at the population level. These broader impacts include benefits to families flowing from prevention of long-term sequelae of infection in children, and to populations and health systems from reduced transmission of infection. Importantly, well-delivered vaccination programs will have a substantial impact by improving equality in health outcomes across populations. Broader impacts include reductions in syndromic disease beyond laboratory-proven infection (e.g., diarrhea and pneumonia), indirect reductions in disease in those not immunized (within and beyond age cohorts targeted by vaccine programs), and improvements in other health services driven by the infrastructure for vaccine delivery. Measurement of these broader impacts can be challenging and must also acknowledge the potential for trade-offs, such as replacement disease due to non-vaccine strains, as documented for pneumococcal infection.
The realization of the benefits of vaccines globally for all children began with the Expanded Program on Immunization (EPI) initiated by the World Health Organization (WHO) in 1974. The EPI focused on improving coverage of six already available but grossly underutilized vaccines—diphtheria–tetanus–pertussis (DTP), polio, measles, and Bacille Calmette–Guerin (BCG). Through the EPI, estimated global coverage for 3 doses of DTP increased from around 20% to over 85%. Subsequent to the EPI, the Global Alliance for Vaccines and Immunization (GAVI), the Global Immunization Vision and Strategy (GIVS), and, most recently, the Global Vaccine Action Plan (GVAP) have aimed to improve access to additional vaccines in the poorest countries. These include Haemophilus influenzae type b (Hib), hepatitis B, pneumococcal conjugate, rotavirus, and human papillomavirus (HPV) vaccines, all introduced in high-income countries from the 1990s. In this chapter, the scope and methodological issues in measuring public health impact are reviewed, estimates of the global public health impact of individual vaccines in children summarized, concluding with potential future benefits to global child health from expanded maternal vaccination and vaccines under development.
Eve Dubé and Noni E. MacDonald
Vaccination is one of the greatest public health successes. With sanitation and clean water, vaccines are estimated to have saved more lives over the past 100 years than any other health intervention. Vaccination not only protects the individual, but also, in many instances, provides community protection against vaccine-preventable diseases through herd immunity. To reduce the risk of vaccine-preventable diseases, vaccination programs rely upon reaching and sustaining high coverage rates, but paradoxically, because of the success of vaccination, new generations are often unaware of the risks of these serious diseases and their concerns now concentrate on the perceived risk of individual vaccines. Over the past decades, several vaccine controversies have occurred worldwide, generating concerns about vaccine adverse effects and eroding trust in health authorities, experts, and science. Gaps in vaccination coverage can, in part, be attributed to vaccine hesitancy and not just to “supply side issues” such as access to vaccination services and affordability.
The concept of vaccine hesitancy is now commonly used in the discourse around vaccine acceptance. The World Health Organization defines vaccine hesitancy as “lack of acceptance of vaccines despite availability of vaccination services. Vaccine hesitancy is complex and context specific, varying across time, place and vaccines.” A vaccine-hesitant person can delay, be reluctant but still accept, or refuse one, some, or all vaccines. Technical, psychological, sociocultural, political, and economic factors can contribute to vaccine hesitancy. At the individual level, recent reviews have focused on factors associated with vaccination acceptance or refusal, identifying determinants such as fear of side effects, perceptions around health and prevention of disease and a preference for “natural” health, low perception of the efficacy and usefulness of vaccines, negative past experiences with vaccination services, and lack of awareness or knowledge about vaccination.
Very few interventions have been shown to be effective in reducing vaccine hesitancy. Most of the studies have only focused on metrics of vaccine uptake and refusal to evaluate interventions aimed at enhancing vaccine acceptance, which makes it difficult to assess their potential effectiveness to address vaccine hesitancy. In addition, despite the complex nature of vaccination decision-making, the majority of public health interventions to promote vaccination are designed with the assumption that vaccine hesitancy is due to lack or inadequate knowledge about vaccines (the “knowledge-deficit” or “knowledge gap” approach). A key predictor of acceptance of a vaccine by a vaccine-hesitant person remains the recommendation for vaccination by a trusted healthcare provider. When providers communicate effectively about the value and need for vaccinations and vaccine safety, people are more confident in their decisions. However, to do this well, healthcare providers must be confident themselves about the safety, effectiveness, and importance of vaccination, and recent research has shown that a proportion of healthcare providers are vaccine-hesitant in their professional and personal lives. Effective strategies to address vaccine hesitancy among these hesitant providers have yet to be identified. A better understanding of the dynamics of the underlying determinants of vaccine hesitancy is critical for effective tailored interventions to be designed for both the public and healthcare providers.