The authority of government to require participation in mandatory childhood vaccination programs may not target specific groups for either participation or exemption on a discriminatory basis. This poses difficulties when allowing religious or philosophical exemptions to mandatory vaccination, because certain groups are more likely to appeal for exemption. Avoiding loss of herd immunity, then, may require either discrimination against these groups by disallowing an exemption option that is available to others, or by denying the good of an exemption option to the entire population because of the action of certain groups. To avoid this unacceptable choice, steps must be taken now to more stringently enforce exemption requirements.