Tuesday, April 07, 2015

Pregnancy, Flu and The Next Pandemic


Photo Credit – CDC


# 9909


During the 1918 pandemic an abnormally high number of pregnant women died from the influenza, and those that survived endured a very high miscarriage rate.  Again, during the much milder 1957 Asian Flu, pregnant women reportedly suffered disproportionately higher mortality rates than non-pregnant women of the same age.


Historical reviews of both events are available in a Perspective, written by 3 CDC physicians (Sonja A. Rasmussen,  Denise J. Jamieson, Joseph S. Bresee) and published in the CDC Journal of EID article, Pandemic Influenza and Pregnant Women in February of 2008.

True to form, the 2009 H1N1 pandemic saw similarly high rates of influenza complications among pregnant women, often with tragic results. 


  • During the 2009 H1N1 pandemic,  pregnant women were six times more likely to be hospitalized than non-pregnant women (see Pregnancy & Flu: A Bad Combination).
  • And in 2011, in BMJ: Perinatal Outcomes After Maternal 2009/H1N1 Infection we saw a study where pregnant women who were admitted to the hospital with an  H1N1 infection experienced a 3 to 4 times higher rate of preterm birth, 4 to 5 times greater risk of stillbirth, and a 4 to 6 times higher rate of neonatal death.


    One problem with these studies has been they are often undertaken either in an ad hoc fashion in the midst of an influenza crisis, or are based on a retrospective look at the data.  While both can provide important clues, a more orderly and well planned study would likely provide better data.


    To that end, researchers in the UK have already designed, and put into `hibernation’ until needed, the framework for just such a study, if and when the next influenza pandemic appears.   First a link to the Abstract (the entire document is available online), then I’ll be back with a bit more.


    Planning for a cohort study to investigate the impact and management of influenza in pregnancy in a future pandemic.


    Knight M, Brocklehurst P, O’Brien P, Quigley MA, Kurinczuk JJ.


    Southampton (UK): NIHR Journals Library; 2015 Mar.
    Health Services and Delivery Research.



    Evidence from the 2009 A/H1N1 influenza pandemic demonstrated that pregnant women are particularly vulnerable to infection and at an increased risk of death. Active data collection through the UK Obstetric Surveillance System (UKOSS) about women admitted to hospital during the 2009 A/H1N1 pandemic was used to inform ongoing clinical guidance regarding the use of antiviral treatment for pregnant women and demonstrated that, in addition to an increased risk of maternal morbidity, influenza infection in pregnancy is associated with poor perinatal outcomes, including an increased risk of stillbirth and preterm birth. This evidence influenced the decision to offer routine influenza immunisation to pregnant women. Even in a non-epidemic period, pregnant women continue to die from influenza.


    To establish, and then to put into hibernation, the study mechanisms needed to mount a rapid investigation of the impact of pandemic influenza in pregnancy in the event of a newly emerging pandemic strain.


    A new UKOSS cohort study was designed, based on the 2009–10 study, and following consultation with the Pandemic Flu Planning Group at the Royal College of Obstetricians and Gynaecologists and the UKOSS Steering Committee, to identify potential previously unanswered questions.


    UK maternity units.


    All pregnant women admitted to hospital with influenza in a future pandemic.


    Management of pregnant women with influenza infection, intervention rates, treatment and pregnancy outcome for both the mother and fetus.


    The study was designed and approved by the UKOSS Steering Committee and then placed into hibernation for activation in the event of an influenza pandemic.


    Pregnant women, as a result of their changed immunological status, appear to be particularly susceptible to infection, including from influenza. The existence of the UKOSS enabled us to rapidly mount a study of pregnant women who were hospitalised with 2009 A/H1N1 influenza. Minor modifications to incorporate previously unanswered questions and our previous study enabled us to design, and then put into hibernation, a new study ready to investigate the impact and management of influenza in pregnancy, which is poised for activation in the event of a newly emerging pandemic strain. This will enable real-time data to be available on which to base rapid changes in clinical management as the as-yet-unforeseen pandemic unfolds. In the event of an influenza pandemic the study will be available to be immediately activated following expedited regulatory approvals.



    We’ve known for a long time that influenza and pregnancy can endanger both the mother and unborn child’s life – and that holds true for both pandemic and seasonal influenza.


    Over the past decade we’ve also seen a handful of studies tentatively linking prenatal exposure to influenza (or an influenza-like-illness) with a variety of child and adolescent development disorders (see Of Pregnancy, Flu & Autism).


    Which explains why the CDC, the WHO, and other public health stress the importance of seasonal flu vaccination for pregnant women every year. 

    Despite all of this evidence of harm from influenza - there remains reluctance among some pregnant women to get the shot. In part, due to the persistent anti-vaccine rhetoric on the internet and in the media - including unfounded claims that the 2009 H1N1 vaccine was responsible for `thousands’ of miscarriages. 


    The science, however, overwhelmingly supports the safety of flu shots for pregnant women.


    In October of 2011, in IDSA: Flu Vaccines In Pregnancy, we saw several studies presented at the 49th Annual Meeting of the Infectious Diseases Society of America (IDSA) reaffirming the benefits and safety of maternal vaccination.The CDC has synopsized these studies in:


    Pregnancy and Influenza Vaccine Safety


    In 2012, in BMJ: H1N1 Vaccination & Fetal Death Rates, we looked at a large cohort study of pregnant women in Demark that reassuringly finds no increase in miscarriage among those who received the 2009 H1N1 vaccine.  Results that mirrored another study  we saw in  Hong Kong: No Increase In Fetal Death Among Vaccine Recipients.


    Ironically, while some seek to demonize the flu vaccine as causing fetal deaths, in October of 2011 in UK: Pregnancy And Swine Flu a study conducted at Oxford University by the National Perinatal Epidemiology unit found a strong link between infection with the 2009 `swine’ flu and an increased number of stillbirths.


    Fetal deaths among women infected with the H1N1 virus were 5 times higher than normal.


    While no drug or vaccine can claim to be 100% safe or benign, the evidence continues to show that flu vaccines are among the safest drugs available, and that most years they can provide decent protection against a serious and potentially deadly illness.


    For pregnant women and their unborn children - the real risks come from influenza virus - not from the vaccine.