Abstract
ObjectiveThis study compared the incidence of rubella seronegativity among gravidae of 25 year-old and younger, between those born in Hong Kong after 1983 when the two-dose rubella vaccination was implemented, versus gravidae born before, to examine the impact of the two-dose regimen.MethodsIn this retrospective cohort study, the incidence of antenatal rubella seronegativity in our parturients managed in1997-2015 was analysed by their age from ≤16 to 25 years, and the effect of year of birth was determined adjusting for confounding factors including teenage status, obstetric history, anthropometric factors, and health parameters including anaemia, thalassaemia trait and hepatitis B carrier status.ResultsAmong the 12743 gravidae, the 6103 gravidae born after 1983 had overall higher rubella seronegativity (9.1% versus 4.4%, OR 2.061, 95% CI 1.797–2.364), with significant difference (p = 0.006) and inverse correlation (p<0.001) with age, in contrast to the 6640 gravidae born in/before 1983 whom there was significant difference (p = 0.027) but a positive correlation (p = 0.008) with age. For each year of age, the former had significantly higher incidence of rubella seronegativity except for those of ≤16 years. Regression analysis confirmed that birth after 1983 was independently associated with rubella seronegativity (aOR 2.207, 95% CI 1.902–2.562).ConclusionThere was a significant trend between rubella seronegativity with age in young gravidae, but the pattern was opposite between gravidae born after versus in/before 1983, with the former having a higher incidence of seronegativity at all ages. Young women covered by the two-dose rubella immunisation programme have a paradoxically higher incidence of rubella seronegativity.
Highlights
The successful implementation of the highly effective mumps-measles-rubella (MMR) vaccine can be best exemplified by the experience in Finland, where the 2-dose schedule introduced since 1982 reduced all MMR diseases to 0.1 per 100,000 population in 1995 [1]
We have previously found that the incidence of rubella seronegativity had decreased from 12.6% in gravidae born in Hong Kong before 1965 to 6.5% in those born after 1983, when each individual would have received two doses at the age of 12 months and 12 years [21]
For this retrospective cohort study approved by the Institutional Review Board (IRB) of The Joint Chinese University of Hong Kong–New Territories East Cluster Clinical Research Ethics Committee (CRE-2009.271), all the data were fully anonymized before access by the researchers, and the IRB has waived the requirement for patient informed consent
Summary
The successful implementation of the highly effective mumps-measles-rubella (MMR) vaccine can be best exemplified by the experience in Finland, where the 2-dose schedule introduced since 1982 reduced all MMR diseases to 0.1 per 100,000 population in 1995 [1]. Mop-up exercises were further conducted annually in primary six to ensure adequate immunization of students against measles. This two dose regime was documented with 99% coverage of all primary six students [13,14], and which would have covered all children born after 1983. The children’s immunisation record would be checked at primary schools for any necessary remedial action [12,14] These measures most likely explained the small number of reported rubella cases of between 19 and 53 from 2001 to 2008, and only one case of congenital rubella syndrome (CRS) in 2008 [15,16]
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