Comparing Rubella Vaccination Strategies in China

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

2. 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

3. China • Population structure • Limited resources • Current practice • What strategy?

5. Outline • Historical lessons • The model • Vaccination strategies • Results • Summary

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

7. Age distribution in 1965 and 1976

8. Age distribution in 1987 and 2000

9. 1990: the model and the data

10. Growth rate with the size

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

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

13. 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+

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

15. Rubella cases: no vaccination

16. CRS cases: no vaccination

17. 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.

18. 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: 15-40 year old women • Combinations of above

19. Rubella cases:

20. CRS cases:

21. Increasing age of attack:

22. 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.

23. Rubella: vaccinate 12 year old girls

24. CRS:vaccinate 12 years old girls

25. 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.

26. 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%

27. Rubella: 2005 Mass campaign + …

28. CRS: 2005 mass campaign + …

29. Rubella: vaccinate 2-14 yr olds in 2005

30. CRS: vaccinate 2-14 yr olds in 2005

31. Conclusions (cont.): • A mass campaign of vaccinating 15-40 year old women can reduce CRS cases during the following 10-20 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.

32. Predicted crs cases:2005-2050

33. Conclusions (cont.) • Best combination strategy seems to be mass vaccination of 2-14 year old children and 15-40 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.