Is the Flu Shot Safe when Trying to Get Pregnant?

We give up drinking alcohol, we switch out our anti-wrinkle and/or acne cream for not so quite effective creams, cut back on eating tuna and may even give up coffee, all in effort to protect our potential pregnancy. So when the news and media share a study that says, 'study shows a hint of a possible link between miscarriage early in pregnancy and flu vaccine', it's natural to be concerned. Why are the Centers for Disease Control and Prevention (CDC) and American College of Obstetricians and Gynecologists (ACOG) still recommending the flu shot and is it safe for pregnancy?


We've come a long way with medical care, which is largely in part due to vaccinations. It is estimated that 17.1 million lives have been saved since year 2000 with the Measles vaccination alone [source]. For the 2015-2016 influenza season, CDC estimates that influenza vaccination prevented approximately 5.1 million influenza illnesses, 2.5 million influenza-associated medical visits, and 71,000 influenza-associated hospitalizations [source]. Also, the CDC reports that 90% of the children that died from influenza during the 2013 flu season were not vaccinated [source]. 


Since pregnant women are at a greater risk for severe illness, it makes sense why there is a push for the flu vaccination by healthcare providers. When a pregnant woman falls ill, as with influenza infection, it can be harmful to both the mother and unborn baby. Prolonged high fever may cause miscarriage in the early stages of pregnancy and premature labor [source]. Note: minor infections, such as a cold, are not harmful [source]. 


Why are Pregnant Women at Greater Risk for the Flu?

When we become pregnant,  we undergo immunological adaptations to support the pregnancy. This leads topotentially having a suppressed immune system and may cause increased susceptibility and/or risk of severe outcomes when pregnant. For example, during the 2009 H1N1 scare, the cause of severe outcomes in pregnant women were linked to low levels of immunoglobulin G antibodies, which often occurs in pregnancy [source].


What About the Recent Study that Shows Potential Risk of Vaccination? 


Scientists analyzed the immunizations of 485 pregnant women who had regular baby deliveries as well as 485 women who had miscarriages during flu seasons in 2010-2011 and 2011-2012. The number of cases that received the flu vaccine to protect against the H1N1 flu virus strain two years in a row, had the most cases of miscarriages. The miscarriage occurred with within 28 days after receiving the shot on average at 7 weeks gestation (see study abstract here).


Why do Health Experts and Organizations Say we Can't Conclude Anything Yet From this Study?

If you look up the research, you will see that the confidence interval has a lot of variability. When there is too much variability in a study, this typically indicates that the study was too small or too many other factors may be interfering to be able to make a meaningful conclusion from the data. In other words, based on the study results, researchers can not know if the vaccine caused the miscarriages or if the findings are simply an association (meaning the miscarriages could be due to something else entirely). For example, one article in Science Magazine ,reports that the cases were significantly older than controls. Miscarriage becomes much more common in women over 35 years old, which researchers even refer to as "advanced maternal age." 

This research study, however, does show that further studies are warranted. The CDC announced it will do a follow-up study on the 2012-2015 influenza seasons. 


Why Should You Get the Flu Vaccine (according to CDC and ACOG)

  • Protects your baby after birth from flu by passing antibodies to developing baby.
  • Vaccination during pregnancy is the most effective strategy to protect newborn babies because the flu vaccine is not approved for use in infants younger than six months [source]. 
  • Pregnant women are significantly more susceptible to illness when pregnant and the flu vaccine may protect you. 
  • The preponderance of data overwhelmingly demonstrate the safety of influenza vaccination during pregnancy (11–15) [source].


ACOG Recommendations:

  • The inactivated influenza vaccine can be given to pregnant women at any point during gestation
  • Live, attenuated influenza vaccine is available as an intranasal spray and is not recommended for pregnant women.
  • Get the shot in time for flu season. In the United States, the influenza season typically occurs from October through May.


What about Thimerosal? 

Thimerosal is deemed safe by major health organizations [source]. Not all experts agree, however, that thimerosal is safe [source]. While health organizations and research show that thimerosal is safe, it has been removed from vaccinations given to children and infants. 


If you are unsure of which vaccination to take or if you are unsure of taking the flu vaccination, talk to your doctor about any concerns you may have.


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