Go big and go fast--vaccine refusal and disease eradication.

D eradication is an attractive public health goal. In addition to eliminating illnesses and deaths, eradication can lead to substantial cost savings. Eradication has been attempted for many human and animal diseases, such as smallpox, malaria, hookworm disease, polio, rinderpest, yaws, dracunculiasis (guinea worm disease), and yellow fever, and many tools have been employed in these efforts. But in the two diseases that were successfully eradicated, smallpox and rinderpest, the main tool was a vaccine. Eradication strategies for polio (a major current focus of global eradication efforts) and measles (whose eradication is being considered) rely on high vaccination coverage through routine and supplementary immunization. Eradication efforts for vaccinepreventable diseases face many challenges, including vaccine refusal. Such refusal in communities in northern Nigeria and Pakistan, for example, has caused major setbacks to global polio eradication, contributing to continued endemic transmission of poliovirus in these countries and to the reintroduction of wild-type poliovirus into countries where transmission had been interrupted. Although wild-type polioviruses are no longer endemic in India, refusal played some role in delaying elimination. The resurgence of measles in Europe, partially attributed to vaccine refusal, threatens its regional elimination and eventual global eradication. It is therefore important to understand the determinants and dynamics of vaccine refusal affecting disease-eradication initiatives. Many factors contribute to the development of clusters of people who refuse vaccines, including changes over time in attitudes toward vaccines. If aggressive control efforts have substantially reduced a disease’s incidence, few people in a given community may have direct (or indirect) experience with that disease. Therefore, successive age cohorts have only a vague collective memory of the disease’s dangers, whereas people may frequently hear about real and perceived adverse effects of vaccination. Parental perception of risks and benefits associated with vaccines is thus altered, and vaccine refusals often increase.1 North American and European countries, for example, have seen substantial reductions in the rates of vaccine-preventable diseases. Since vaccines against measles, mumps, rubella, and diphtheria were introduced in the United States, their incidence has been reduced by more than 99%, and the incidence of tetanus has fallen by 94% since routine tetanus vaccination began.2,3 These decreases have coincided with increases in vaccine refusal in the United States and Europe. The notion that vaccine acceptance is influenced by rates of vaccine-preventable diseases is supported by theories from behavioral sciences. For example, a useful framework for understanding vaccine acceptance is the health-belief model, according to which the uptake of a health intervention is associated with perceived susceptibility to and severity of the relevant disease and the intervention’s safety and efficacy. Empirical studies have validated this model as a predictor of vaccine refusal. In the context of eradication, reduction in disease incidence reduces the perceptions of susceptibility to disease and its complications, diminishing an important motivation for accepting a vaccine. It is often assumed that this phenomenon does not apply to low-income countries where there is increasing opposition to vaccines, despite the high burden of infectious diseases. This perspective misses an important point: perceptions regarding vaccines are often vaccine-specific and disease-specific. For example, in high-income countries, although many parents have generalized concerns regarding immunization, perceptions of specific vaccines vary considerably. Similarly, the more prominent instances of vaccine refusal in low-income countries have been specific to vaccines for diseases with actual or perceived low incidence. Refusal of the polio vaccine in northern Nigeria and parts of northern India, for instance, was vaccinespecific: communities that refused polio vaccine were still demanding measles vaccines. In fact, the low polio rates, achieved through intensive immunization efforts in previous years, were a reason why many did not consider polio eradication a priority: “Some people have never even seen polio, but yet they keep giving us medicine for it,” one Nigerian told a researcher. “If you look around it is hard to find 2 or 3 people with polio, but it is easy to go to the hospital and find 50 people sick with no money to buy the medi-