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Fighting the Flu During Pregnancy

Katlyn Joy | 9, February 2015


A commonly held belief about a woman's immune system being weaker during pregnancy, and therefore, increasing her risk from the flu has come under fire after recent research out of Stanford Univers

A report published in the September Proceedings of the National Academy of Sciences asserts the opposite is the actual truth; pregnant women face more dire effects from influenza not because their immune system is weak, but rather because their immune system reaction is too strong.

The costs are critically high, as well. During the 2009 H1N1 pandemic, pregnant women bore an elevated risk. They made up 5 percent of the flu deaths, even though they were only 1 percent of the population.

For the study researchers took blood samples from both pregnant and non-pregnant women, and exposed the samples to the influenza A virus. What researchers observed was two types of immune cells, T cells and natural killers, became supercharged, producing more molecules in the response to the virus. Basically, a protective response from the body goes overboard and actually goes from protecting to harming a woman.

Catherine Blish, assistant professor of infectious diseases at Stanford School of Medicine and the study's senior author says, "Having too many immune cells in the lung can cause inflammation that makes it hard to breathe."

Inflamed tissue in the lungs causes difficulty breathing for any person, but it's probably worse for pregnant women, who already are coping with the cramping of the lungs by a growing fetus. Pregnant women are stricken more often with pneumonia as a complication of the flu. This heightened response at the less alarming end of the scale may also be why pregnant women tend to feel worse when suffering through a case of influenza.

While Blish and the other Stanford researchers intend to do further testing to see whether other viruses cause the same reaction and whether it could be possible to dial down the immune response in severe flu cases, Blish makes this strong recommendation to pregnant women, "The most important thing to remember is that influenza vaccine is really the best tool to prevent infection in the first place."

Currently, only half of all pregnant women get the flu shot. However, it's not just the mother's health at stake; getting the flu vaccine provides protection to her fetus and the baby even after birth, when the child is too young to get the shot. Not only that, but it's been shown that in mothers who got the flu shot, there is less risk of her giving birth prematurely or having a child with low birth weight.

For those concerned about the safety of a flu shot in pregnancy should know that millions of women who are pregnant have been getting the flu vaccine for many years. Flu shots have never been linked to adverse or serious reactions in pregnant women. The minor side effects possible are a soreness or redness at the site of the injection.

Some questions have been raised about the safety of flu vaccines, particularly for pregnant women, since they've heard of them containing the mercury-based preservative thimerosal. Thimerosal is present in trace amounts in some vaccines, particularly the multidose vials to prevent contamination with germs, fungi and bacteria. Single-dose vials do not contain thimerosal.

While the best and most recent research shows no elevated risks from vaccines with the preservative, you can always ask your physician to use a single dose vial which is thimerosal-free.

Getting a flu shot will offer protection to a pregnant woman's child, up to six month of age. However, pregnant women need the injection and should not receive the nasal spray vaccine.

The Centers for Disease Control and Prevention warn that if you do not get the vaccine and show signs of the flu you must seek immediately medical attention. Having a fever, flu or other illness can cause birth defects in your unborn child.

These symptoms warrant a trip to the doctor right away in pregnant women:

  • Shortness of breath
  • Trouble breathing
  • Pain or pressure in the abdomen or chest
  • Confusion
  • Sudden dizziness
  • Vomiting that is severe or persistent
  • Fever that doesn't respond to acetaminophen
  • Decreased or absent movement of the baby

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