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Who is at Highest Risk for Complications from Influenza Vaccine?


The Institute of Medicine has acknowledged that there is individual susceptibility to vaccine reactions for genetic, biological and environmental reasons but that vaccine providers cannot accurately predict prior to a vaccine’s administration who will suffer complications, injury or death from vaccination. 1 However, a person who has previously had a serious reaction to a vaccination or is acutely or chronically ill should become informed about all potential risks associated with vaccination and discuss any concerns with a trusted health care professional before receiving influenza vaccine or any other vaccine.

Currently, a history of GBS or a severe allergy to a vaccine component or history of a life threatening allergic reaction to a previous flu shot are the only CDC approved official contraindications (medical reasons for not getting vaccinated) to receiving inactivated influenza vaccines.2 However, the CDC also states that influenza vaccination should be postponed if a child or adult has “moderate or severe acute illness with or without a fever,” which is listed as a “precaution” for receipt of any vaccine. 3

Is Flu Vaccine Recommended for Children? 

One consideration with the recommended widespread administration of annual flu shots to all children over six months of age is interference with the acquisition influenza antibodies acquired after recovery from type A or B influenza infections. The question of whether it is better for healthy children, who rarely suffer complications from flu, to get the flu and develop permanent immunity to that flu strain or it is better for children to get vaccinated every year to try to suppress all flu infection in early childhood is a question that has yet to be adequately answered by medical science.

Although in the past the flu vaccine has not been recommended for healthy children, today vaccination of children between the ages of 6 months and 18 years is strongly recommended by the Advisory Committee on Immunization Practices (ACIP) of the CDC4 and New Jersey now requires influenza vaccine for daycare and kindergarten entry.5

Is influenza vaccine safe during pregnancy?

In years past, pregnancy was also a contraindication to flu vaccine but, today, the Advisory Committee on Immunization Practices (ACIP) of the Centers for Disease Control (CDC) recommends flu vaccine for all pregnant women.6

Initially, most Influenza vaccines were classified as Category B or C drugs, which means that adequate and well-controlled studies on pregnant women have not been conducted and it is not known whether these vaccines can cause fetal harm when administered to a pregnant woman or if they can affect reproduction capacity.7 

In 2015, the FDA removed pregnancy categories due to concerns of confusion and oversimplification and replaced it with the Pregnancy and Lactation Labeling Rule.8 This rule affects all influenza vaccine products submitted for approval after June 30, 2015. As new language is phased in, information on risks associated with vaccinating while pregnant will appear in 8.1 of each vaccine’s product insert under Risk Summary. NVIC encourages consumers read this information carefully prior to receiving a vaccine.

Prior to the FDA licensing of all influenza vaccines, drug companies did not test the safety and effectiveness in pregnant women9 and little data is available on biological responses to these vaccines that could affect pregnancy and birth outcomes.10

Pregnant women should also be aware that the multi-dose flu vaccine contains Thimerosal, which is a mercury derivative. Mercury is toxic to the brain and has been found to be associated with brain damage and developmental delays in babies whose mothers were exposed to high levels of mercury during pregnancy.11,12

In December 2016, Congress signed the 21st Century Cures Act into law. This new law protects vaccine manufacturers from lawsuits in civil court if an FDA licensed vaccine given to a pregnant woman causes the injury or death of her unborn child in the womb.13 14 As a result, policies relating to compensating vaccine injuries sustained by an unborn child in the womb are being developed.

In 2017, a Centers for Disease Control (CDC) funded study reported that women vaccinated in the early part of their pregnancy with a flu vaccine containing the pandemic H1N1 (H1N1pdm09) strain who also had been previously vaccinated during the prior flu season with a  H1N1pdm09-containing flu vaccine had a greater risk of miscarriage in the first four weeks following vaccination. The CDC is in the process of conducting further research among women who were pregnant during the 2012-2013 through 2014-2015 flu season and eligible to receive the flu vaccine. Results of this study are expected in late 2018 or 201915. Despite concerns regarding the safety of flu vaccination during pregnancy, the CDC continues to recommend the flu vaccine for all pregnant women at any point during pregnancy16.

What about mercury in the influenza vaccine?

In 1999, the Environmental Protection Agency (EPA) and the Food and Drug Administration (FDA)17 directed the vaccine manufacturers to take mercury out of all childhood vaccines.

In October 2001, the Institute of Medicine issued a report that said it is "biologically plausible" that mercury-containing vaccines could cause injury to the brain but there have been “too few scientific studies conducted to prove conclusively that mercury in vaccines has caused brain damage.”18

Nevertheless, the Institute of Medicine recommended that drug companies take all mercury out of all vaccines and over-the-counter drugs.

In compliance with this recommendation a preservative-free vaccine formulated for children ages 6 to 35 months, with only a trace amount of thimerosal, is available in a limited amount. It is distinguished by a pink syringe plunger rod in the pre-filled syringe or in a single dose vial.  All multi-dose vials of influenza vaccine contain thimerosal.

Many influenza vaccines in the U.S. also contain the mercury preservative, Thimerosal, in amounts above federal safety guidelines. Thimerosal free influenza vaccine is also licensed in the U.S. and it is advisable to request these vaccines in advance from your healthcare provider, if your preference is the Thimerosal free version. Click here to determine which vaccines are thimerosal free.

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1  Institute of Medicine Committee to Review Adverse Effects of Vaccines. Adverse Effects of Vaccines: Evidence and Causality: Evaluating Biological Mechanisms of Adverse Events (p. 57-102), Increased Susceptibility (p. 82). Washington, DC: The National Academies Press 2012.

2  CDC. Seasonal Influenza Vaccine Safety - A Summary for Clinicians: Contraindications and Precautions. Oct. 3, 2017.

3  CDC. Vaccine Recommendations and Guidelines of the ACIP: Contraindications and Precautions. July 18, 2018.

4 CDC. Prevention and Control of Seasonal Influenza with Vaccines: Recommendations of the Advisory Committee on Immunization Practices — United States, 2016–17 Influenza Season. MMWR Aug. 26, 2016; 65(5);1–54.

5 Alfonsi S. N.J. Mandatory Flu Shots for Preschoolers Cause Outrage. ABC News Oct. 17,2008.

6 CDC. Flu Vaccine Safety and Pregnancy. Oct. 3, 2017

7 U.S. Dept. of Health & Human Services. FDA Pregnancy Categories. Sept. 29, 2017

8 FDA. Pregnancy and Lactation Labeling (Drugs) Final Rule. Jun. 28, 2018

9 Gruber MF. Maternal Immunization: US FDA Regulatory Considerations (Abstract). Vaccine 2003; 21(24): 3487-3491.

10 Christian LM, Iams JD et al. Inflammatory Responses to Trivalent Influenza Virus Vaccine Among Pregnant Women. Vaccine 2011; 29(48): 8982-8987.

11 Ayoub D Yazbak FE. Influenza vaccination during pregnancy: A critical Assessment of the Recommendations of the Advisory Committee on Immunization Practices (ACIP). Journal of American Physicians & Surgeons 2006; 11(2): 41-47.

12 Elce D, Celik A. Genotoxicity of thimerosal in cultured human lymphocytes with and without metabolic activation sister chromatid exchange analysis proliferation index and mitotic index. Toxicology in Vitro June 2008; 22(4): 927-934.

13 Businesswire. National Vaccine Information Center (NVIC) Calls 21st Century Cures Act “A Wolf in Sheep’s Clothing” and Urges Presidential Veto to Protect Public Health. NVIC Press Release: Dec. 8, 2016.

14 Feemster KA. Advisory Commission on Childhood Vaccines Maternal Immunization Working Group Draft Recommendations. ACCV June 7, 2013.

15 CDC. Flu Vaccination & Possible Safety Signal. Sep. 13, 2017

16 CDC. Flu Vaccine Safety and Pregnancy. Oct. 3, 2017

17 FDA. Thimerosal in Vaccines. Recent and Future FDA Action. Feb. 2, 2018.

18 Institute of Medicine Committee to Review Adverse Effects of Vaccines. Immunization Safety Review: Thimerosal - Containing Vaccines and Neurodevelopmental Disorders. Washington, D.C. The National Academies Press 2001.

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