KEYWORDS:
Childhood immunization, health policy, collective action, mandatory vaccination, comparative study

BACKGROUND:
The worldwide effort to vaccinate children against infectious disease represents one of the most successful public health programs in history. The program in the United States has been particularly successful, given the limited exemptions available to opt children out of mandatory vaccination prior to entering day care and public school settings. The success of the programs, however, also create conditions that threaten to undermine their effectiveness. Specifically, the fact that widespread childhood vaccination has eliminated or drastically reduced the incidence of many once-common diseases, means that any one parent's failure to have their child vaccinated does not translate into a high risk of contracting a vaccine-preventable disease. The reason for this is that for most vaccine preventable diseases, herd immunity has been achieved, protecting those who opt out of vaccination. Herd immunity, however, can only be maintained if the percentage of people who decide to opt out remains low. These facts result in a number of classic collective action problems, which we will examine in detail.

OBJECTIVE:
To discuss how the problem of collective action, and the structure and enforcement of vaccination laws and policies, presents challenges to maintaining high rates of childhood vaccination.

METHOD:
Examination of philosophical and legal foundations of childhood vaccination law in the U.S. and the United Kingdom, and the challenges the collective action problem presents thereto.

RESULT:
In the United Kingdom, classic collective action problems are helping drive the current crisis over maintaining herd immunity against measles. Collective action problems have also contributed to increased vulnerability of some populations in the United States as well.

CONCLUSION:
Collective action problems may already be undermining efforts to maintain high rates of childhood immunization in the United Kingdom, and increased concern about vaccine side-effects, coupled with increasing leniency of vaccination exemption policies, may raise similar risks in the United States.

LEARNING OBJECTIVES:
To describe collective action problems arising in the context of U.S. and United Kingdom childhood vaccination policies.