Predicting and comparing long-term measles antibody profiles of different immunization policies.
OBJECTIVE
Measles outbreaks are infrequent and localized in areas with high coverage of measles vaccine. The need is to assess long-term effectiveness of coverage. Since 1991, no measles epidemic affecting the whole island has occurred in Taiwan, China. Epidemiological models are developed to predict the long-term measles antibody profiles and compare the merits of different immunization policies on the island.


METHODS
The current measles immunization policy in Taiwan, China, is 1 dose of measles vaccine at 9 months of age and 1 dose of measles, mumps and rubella (MMR) vaccine at 15 months of age, plus a 'mop-up' of MMR-unvaccinated schoolchildren at 6 years of age. Refinements involve a change to a two-dose strategy. Five scenarios based on different vaccination strategies are compared. The models are analysed using Microsoft Excel.


RESULTS
First, making the assumption that measles vaccine-induced immunity will not wane, the predicted measles IgG seroprevalences in preschool children range from 81% (lower bound) to 94% (upper bound) and in schoolchildren reach 97-98% in all strategy scenarios. Results are dependent on the association of vaccine coverage between the first and second dose of vaccine. Second, if it is assumed that vaccine-induced antibody titres decay, the long-term measles seroprevalence will depend on the initial titres post vaccination, decay rates of antibody titres and cut-off of seropositivity.


CONCLUSIONS
If MMR coverage at 12 months of age can reach > 90%, it would be worth changing the current policy to 2 doses at 12 months and 6 years of age to induce higher antibody titres. These epidemiological models could be applied wherever a similar stage of measles elimination has been reached.
Lee
M S
MS
Wellcome Trust Centre for the Epidemiology of Infectious Disease, Oxford University, England. mslee007@us.sina.com
Nokes
D J
DJ
D000293:Adolescent; D000914:Antibodies, Viral / Q000097:blood*; D002648:Child; D002675:Child, Preschool; D005544:Forecasting; D006291:Health Policy; D006801:Humans; D017589:Immunization Programs; D007115:Immunization Schedule; D007074:Immunoglobulin G / Q000008:administration & dosage* / Q000276:immunology; D008457:Measles / Q000453:epidemiology / Q000276:immunology* / Q000517:prevention & control; D008458:Measles Vaccine / Q000008:administration & dosage* / Q000276:immunology; D008459:Measles virus / Q000276:immunology*; D016036:Seroepidemiologic Studies; D013624:Taiwan / Q000453:epidemiology; D016896:Treatment Outcome
D000914:Antibodies, Viral; D007074:Immunoglobulin G; D008458:Measles Vaccine