Timeliness of childhood vaccination in the Federated States of Micronesia

Abstract

Background: Vaccination coverage is typically measured as the proportion of individuals who have received recommended vaccine doses by the date of assessment. This approach does not provide information about receipt of vaccines by the recommended age, which is critical for ensuring optimal protection from vaccine-preventable diseases (VPDs). Objective: To assess vaccination timeliness in the Federated States of Micronesia (FSM), and the projected impact of suboptimal vaccination in the event of an outbreak. Methods: Timeliness of the 4th dose of diphtheria, tetanus, and acellular pertussis vaccine (DTaP) and 1st dose of measles, mumps, and rubella vaccine (MMR) among children 24–35 months was assessed in FSM. Both doses are defined as on time if administered from 361 through 395 days in age. Timeliness was calculated by one-way frequency analysis, and dose delays, measured in months after recommended age, were described using inverse Kaplan-Meier analysis. A time-series susceptible-exposed-infected-recov ery (TSEIR) model simulated measles outbreaks in populations with on time and late vaccination. Results: Total coverage for the 4th dose of DTaP ranged from 36.6% to 98.8%, and for the 1st dose of MMR ranged from 80.9% to 100.0% across FSM states. On time coverage for the 4th dose of DTaP ranged from 3.2% to 52.3%, and for the 1st dose of MMR ranged from 21.1% to 66.9%. Maximum and median dose delays beyond the recommended age varied by state. TSEIR models predicted 10.8–13.7% increases in measles cases during an outbreak based on these delays. Conclusions: In each of the FSM states, a substantial proportion of children received DTaP and MMR doses outside the recommended timeframe. Children who receive vaccinations later than recommended remain susceptible to VPDs during the period they remain unvaccinated, which may have a substantial impact on health systems during an outbreak. Immunization programs should consider vaccination timeliness in addition to coverage as a measure of susceptibility to VPDs in young children.

Descriptive analysis of routine childhood immunisation timeliness in the Western Cape, South Africa

“…The lack of a standard definition of delayed immunisation contributes to the complexity of quantifying delay and determining reasons for delay [18] . Despite the lack of a standard definition, generally delay in immunisations based on studies conducted in LMICs, has been described as ≥ 4 weeks (28 days) deviation from the EPI schedule [20] , [21] , [22] , [23] .…”

Vaccination timeliness and delay in low- and middle-income countries: a systematic review of the literature, 2007-2017

“…52 Finally, 4 papers (7%) evaluated timeliness in terms of the interval which elapsed between doses rather than the date of vaccination itself, which would result in 'timely' vaccination calculations if the first vaccine in the series was initiated late but all subsequent vaccines were given within the recommended interval. 21,23,73,84…”

Trends of infant vaccination timeliness and completion in selected urban slum communities in Ibadan, Southwestern Nigeria: A four-year review

“…For an effective infant immunization, both the timeliness of the vaccines and the completion of the vaccination courses are important [ 12 , 13 ]. It is important that all infants complete their immunization schedule because this ensures protection from vaccine preventable diseases as well as herd immunity for these diseases.…”