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Flu vaccine during pregnancy – protects the infant

The modern healthcare system of developed countries have done an outstanding job in reducing the burden of infectious diseases over the past few decades. However, some susceptible groups, such as infants, remain at significant risk to these diseases. Research has recently shown that the flu vaccine during pregnancy protects infants from that disease. This is more data that provides evidence that getting vaccinated, even during pregnancy, is important to infant health.

In a new paper published in Pediatrics, by Dr. Julie H. Shakib et al. of the University of Utah Medical School Department of Pediatrics, examined the health of infants born to influenza-immunized mothers. The short version is that the babies born to these mothers had a smaller number of laboratory confirmed influenza infections and fewer hospitalizations compared to infants born to non-immunized mothers.

I could almost stop there, bold, underline and italicize those results, and move to another article. Lucky for me, the readers of this blog demand real data to support the above conclusion. And I’m here to do just that.

Flu vaccine during pregnancy results

The study used an retrospective cohort epidemiological methodology, which examines  a cohort of individuals that share a common exposure factor to determine its influence on the development of a disease, while comparing that cohort to another group of equivalent individuals that were not exposed to that factor, in this case, flu vaccination status.

The study included data from 245,386 mothers and 249,387 infants between 2005 to 2014 from Intermountain Healthcare Facilities in Utah and Idaho. As studies go, this is a very large number which is important to see even small differences between groups.

Intermountain Healthcare is an integrated medical system, where nearly all medical records are electronically stored, allowing for quick access to data. The researchers surveyed those electronic records to establish maternal influenza immunization status, laboratory-confirmed infant influenza-like illnesses, as well as infant hospitalizations.

Of the nearly 250,000 mothers, only 10% had received the influenza vaccination during their pregnancy. Maybe this research will improve that rate, because the results of this study solidly back flu immunization during pregnancy.

The researchers found that mothers who received government insurance (such as Medicaid) or no insurance, lived in rural areas, or delivered their babies in the Southwest or Urban South were more like to not have been vaccinated.

The study presented several important results:

  •  A total of 32 infants of immunized mothers reported influenza-like illnesses versus 834 infants of unvaccinated mothers. The relative risk for infants of immunized mothers was 0.36 compared to infants from non-immunized mothers. (Relative risk is a statistical measurement that provides us with information on the risk between the two groups – in this case, infants of immunized mothers had about 36% the risk of non-immunized mothers for contracting flu-like illnesses.)
  • Hospitalizations were seen in 4 maternal-immunized infants compared to 237 non-maternal-immunized infants, a relative risk of 0.16
  • Laboratory-confirmed influenza was reported in 20 maternal-immunized infants and 638 in the non-immunized group, a relative risk of 0.30.

In each comparison, the relative risk was substantially lower for infants from immunized mothers. In fact, for hospitalizations, the risk reduction was nearly 84 percentage points.


To simplify these results, infants born to influenza-immunized mothers had fewer reported influenza-like events, a smaller amount of laboratory-confirmed episodes of influenza, and fewer hospitalizations in the first 6 months than infants born to mothers who were not immunized.

This is a very high quality study, with large population numbers and clinically significant results. It is clear that mothers who receive the flu vaccine during pregnancy protect their newborns from the flu, and substantially lower the risk of hospitalization of those babies from the flu.

This is a powerful study that provides straightforward evidence that the flu vaccine is much more important than believed by many. And any pregnant mother should seriously consider the vaccine to give their babies a healthy start to life.

I cannot say this enough – vaccines save lives of babies.

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Michael Simpson

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