Comparing Rubella Vaccination Strategies in China

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Comparing Rubella Vaccination Strategies in China

• Linda Q. Gao
• North Central College

• Herbert Hethcote
• The University of Iowa

May 18, 2004 DIMACS
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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

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China

• Population structure
• Limited resources
• Current practice
• What strategy?

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Outline

• Historical lessons
• The model
• Vaccination strategies
• Results
• Summary

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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

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Age distribution in 1965 and 1976
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Age distribution in 1987 and 2000
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1990 the model and the data
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Growth rate with the size
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The impact of one-child policy on population
age structure
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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

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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

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Seropositivity the model vs. data (with no
vaccination)
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Rubella cases no vaccination
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CRS cases no vaccination
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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.

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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

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Rubella cases
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CRS cases
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Increasing age of attack
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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.

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Rubella vaccinate 12 year old girls
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CRSvaccinate 12 years old girls
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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.

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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

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Rubella 2005 Mass campaign
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CRS 2005 mass campaign
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Rubella vaccinate 2-14 yr olds in 2005
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CRS vaccinate 2-14 yr olds in 2005
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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.

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Predicted crs cases2005-2050
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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.