Comparing Rubella Vaccination Strategies in China Linda Q. Gao North Central College Herbert Hethcote The University of Iowa May 18, 2004 DIMACS

Background: Rubella: mild childhood infectious disease Congenital Rubella Syndrome: severe consequence when pregnant women are infected Vaccination status: 1969 – now WHO recommendations on Rubella/CRS control

China Population structure Limited resources Current practice What strategy?

Outline Historical lessons The model Vaccination strategies Results Summary

China Demographic Model Derived 1965 age distribution from 1987 age distribution data. Used the birth/death rate from as the scaling factor for fertility and death rate. Interpolate fertility and death rate between 1992 and 2000 data. Used Leslie matrix population model

Age distribution in 1965 and 1976

Age distribution in 1987 and 2000

1990: the model and the data

Growth rate with the size

The impact of “one-child” policy on population age structure

M V SEI R The epidemiological model: 58 age groups: 0,1,2,…,49, 50-54, 55-59, …, 75-79, 80-84, 85+ Used proportionate mixing

Parameter values: average passive immunity period is 6 months (182.5 days) average latent period is 10 days average infectious period is 12 days force of infection values:.20 for 0,.24 for 1-4,.27 for 5-9,.15 for 10-14,.10 for 15-49,.04 for 50-64,.03 for 65+

Seropositivity: the model vs. data (with no vaccination)

Rubella cases: no vaccination

CRS cases: no vaccination

Conclusions: One child policy => changing demographics => average age of infection increases => more rubella in pregnant women. Between 2005 and 2050, CRS may increase by a 3 to 5 factor if there is no rubella vaccination.

Vaccination Strategies Vaccinate 1 year old children Vaccinate 12 year old girls Mass campaign: target at 2-14 year old Mass campaign: target at 2-14 year old girls Mass campaign: year old women Combinations of above

Rubella cases:

CRS cases:

Increasing age of attack:

Conclusions (cont.): Routine vaccination of 1 year olds decreases rubella cases CRS cases increases unless > 40% are vaccinated. CRS cases would not decrease significantly until at least 70% are vaccinated. CRS will be eliminated if >80% are vaccinated.

Rubella: vaccinate 12 year old girls

CRS:vaccinate 12 years old girls

Conclusions (cont.): Routine vaccinations of 12 yr old girls are effective per vaccination in reducing CRS This strategy will never lead to elimination of rubella.

Conclusions (cont.) If the achievable vaccination rate is not high, use the strategy of vaccinating 12 years old girls for direct protection. If the achievable vaccination rate can reach a high level, use the strategy of vaccinating 1 years old to eliminate the disease The threshold for switching: about 80%

Rubella: 2005 Mass campaign + …

CRS: 2005 mass campaign + …

Rubella: vaccinate 2-14 yr olds in 2005

CRS: vaccinate 2-14 yr olds in 2005

Conclusions (cont.): A mass campaign of vaccinating year old women can reduce CRS cases during the following years. A mass campaign of vaccinating 2-14 year old children only can lead to large oscillations in CRS cases with peaks above the no-vaccination levels.

Predicted crs cases:

Conclusions (cont.) Best combination strategy seems to be mass vaccination of 2-14 year old children and year old girls/women to provide good short term protection plus routine vaccination of at least 90% of 1 year old children to move towards elimination of rubella in China.