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					   Comparing Rubella Vaccination
   Strategies in China

    Linda Q. Gao               Herbert Hethcote
North Central College        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 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
The epidemiological model:
       M     S     E    I     R


             V


   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
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.

				
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posted:10/11/2011
language:English
pages:33