Table 1.

Immunization Registry characteristics of Colorado, Massachusetts, Missouri and Washington

Registry Characteristic [19]	Colorado	Massachusetts	Missouri	Washington
Catchment area	Regional	Regional	Statewide	Statewide
Provisions for participation	Opt-out	Opt-in	Opt-out	Opt-out
Populated by birth data?	Yes	No	Yes	Yes
Child participation level a	43%	7%	81%	76%
% of public providers enrolled in registry	89%	84%	100%	86%
% of enrolled public providers submitting data within past 6 months	62%	67%	78%	99%
% of private providers enrolled in registry	30%	3%	22%	44%
% of enrolled private providers submitting data within past 6 months	57%	100%	38%	98%
Registry Legislation [20]
State law authorizing immunization registry	Yes	No	No	No
State law mandate reporting?	No	N/A	N/A	N/A
Type of consent needed to enter the registry	Implied consent	Written consent	Implied consent	Implied consent
If implied consent, are there provisions to opt out or limit access to the registry?	No	N/A	No	Yes

^a Child participation level is defined as the proportion of children less than 6 years of age in the catchment area who are enrolled in the registry with 2 or more immunizations recorded.