Comparing Rubella Vaccination Strategies in China

Linda Q. Gao North Central College

Herbert HethcoteThe 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

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

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

S E I 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: 15-40 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 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.

Predicted crs cases:2005-2050

Table 1. Comparison of rubella vaccination strategies in China in 2005 to 2051mass: mass: mass: routine: routine: total CRS CRS # of vaccinations

2-14 girls 2-14 boys 15-40 1 yr old 12 yr old cases cases # of routine # of mass total # of per CRS casewomen children girls 2005-2051 2051 vaccinations vaccinations vaccinations prevented

90% 90% 60% 90% 1,463 0 596,350,831 395,198,054 991,548,885 2,61490% 90% 90% 3,423 0 596,350,831 227,438,932 823,789,763 2,18390% 60% 90% 4,674 0 596,350,831 277,610,095 873,960,926 2,324

70% 90% 8,173 0 596,350,831 195,718,976 792,069,807 2,12690% 90% 10,722 0 596,350,831 109,850,973 706,201,804 1,909

90% 20,757 0 596,350,831 596,350,831 1,65780% 27,308 1 530,089,627 530,089,627 1,50070% 100,970 2,247 463,828,423 463,828,423 1,658

90% 117,602 1,722 308,049,956 308,049,956 1,17160% 276,978 8,139 397,567,220 397,567,220 3,831

90% 296,975 10,904 109,850,973 109,850,973 1,31190% 90% 332,452 10,682 227,438,932 227,438,932 4,710

80% 345,807 11,386 223,678,829 223,678,829 6,40350% 358,881 11,387 139,799,268 139,799,268 6,395

50% 362,752 12,453 331,306,016 331,306,016 18,4170 380,741 11,389 010% 399,712 12,307 66,261,203 66,261,20340% 406,976 13,910 265,044,813 265,044,81320% 413,971 13,143 132,522,407 132,522,40730% 419,181 13,701 198,783,610 198,783,610

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.