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Influenza Vaccination in Pregnancy: Current evidence and selected national policies

Influenza Vaccination in Pregnancy: Current evidence and selected national policies. Lancet Infectious Disease 2008:8: 44-52 Summary By Dr Ng YY. Flu n pregnancy. Pregnant women are more vulnerable during pandemic influenza

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Influenza Vaccination in Pregnancy: Current evidence and selected national policies

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  1. Influenza Vaccination in Pregnancy: Current evidence and selected national policies Lancet Infectious Disease 2008:8: 44-52 Summary By Dr Ng YY

  2. Flu n pregnancy Pregnant women are more vulnerable during pandemic influenza • 4 X higher risk of maternal death during severe season as compared to regular season • Hospitalized pregnant women with respiratory illness had higher odds of • Preterm delivery • Fetal distress • Cesarean section (as compared to hospitalized pregnant females without respiratory illness)

  3. Pregnancy n co-morbidities • 3x more likely to have resp illness during flu months as compared to healthy pregnant women • Highest rate of hospital admission in pregnant females with history of asthma

  4. 1918-1919 Pandemic 20 million deaths with pregnant women at high risk for complications/death Maryland 1350 pregnant female n flu: • Overall case fatality: 27% • Case fatality with pneumonia: 54% Chicago 101 hospitalized pregnant female n flu • Overall case fatality: 32% • Case fatality with pneumonia: >50%

  5. 1957-1958 pandemic: New York: 216 Influenza deaths 22 deaths in unvaccinated pregnant women (7 had rheumatic heart disease) England and Wales: similar doubling risk Minnesota, USA 11 deaths in unvaccinated pregnant women contributed to 50% of maternal mortality (all had fulminant, haemorrhagic pulmonary oedema)

  6. Risk to fetus Transplacental transmission of flu virus: RARE No IgM anti-flu antibodies in cord sera of 138 infants whose mothers had positive serology

  7. Risk to neonate from maternal infection Hospital admission rates: • Lowest for < 5 months old • Highest for > 6 - 23 months old

  8. Flu vaccine • Antibody response to flu vaccine similar in pregnant and non-pregnant women • 87-99% transplacental transfer of flu-specific maternal antibodies • Cord titers did not differ significantly if maternal vaccination in 2nd or 3rd trimester • Half life of antibodies in babies: 43-53 days • Infants < 6 mths less likely to have resp illness when born to immunized pregnant women

  9. 3rd trimester vaccination Significant protection for mother and child From febrile respiratory illnesses ( randomized effectiveness trial of maternal flu immunization in 3rd trimester)

  10. Vaccine safety 1959-1965 US Collaborative Perinatal Project • First trimester influenza vaccination not associated with minor or major malformations in 2 studies (650 mother –child pairs and 50,897 pregnant women) Followed up to age 7 years old for hearing impairment, learning disabilities and malformations • All trimester vaccination not associated with excess childhood malignancies ( 2291 pregnant women and children followed up to 4 years old)

  11. Vaccine safety 1998-2003 historical cohort database in Texas • 2nd and 3rd trimester vaccination • 252 pregnant women • Followed up for 42 days post vaccination No difference in outcomes • of pregnancy • infant hospital admission up to 6 months old Compared to matched unvaccinated healthy controls

  12. Adverse effects • No serious adverse effects of flu vaccination in pregnancy • Mild fever 1.3% • Flu like symptoms • Headache • Dizziness

  13. Thiomersal vaccine • Flu vaccine containing thiomersal (an organic mercury compound used since 1930s as a preservative in vaccines) not contraindicated in pregnant women • No association with neurodevelopmental disorders or autism

  14. Limited safety data in 1st trimester • 1366 reports of adverse reactions to flu vaccine • 8 occurred in pregnancy ( 7 vaccinated in 1st trimester • 1 stillbirth • 3 spontaneous abortions • 3 fetal growth retardation of which 2 delivered prematurely)

  15. Pregnancy associated with higher morbidity and mortality from influenza infection WHO recommendation: ALL PREGNANT WOMEN during flu season Singapore No routine recommendation USA CANADA AUSTRALIA: Vaccinate all pregnant women in any trimester UK: Vaccinate pregnant women with high risk co-morbidity in any trimester Germany Avoid 1st trimester vaccination Flu Immunization

  16. Conclusion Evidence to support flu vaccination • Healthy pregnant women in 2nd and 3rd trimester • Pregnant women with co morbidities in any trimester As pregnant women are more vulnerable

  17. Conclusion • No serious adverse effect of flu vaccination - limited data on safety in 1st trimester • Significant protection during third trimester immunization • Vaccines containing thiomersal not contraindicated in pregnant women • Preference for thiomersal free flu vaccine - precautionary measure only

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