The U.S. Centers for Disease Control and Prevention recommends that almost everyone — including pregnant women — get the injection, despite written warnings from the vaccine manufacturers.
Citing an estimated 36,000 deaths a year from the flu and flu-related illness, the mainstream medical community, including the American Academy of Pediatrics and American Lung Association, says the benefits far exceed any risk from the shot.
In a typical year, between 5 percent and 10 percent of the population will get the flu virus, resulting in roughly 200,000 hospitalizations, according to the CDC. The flu can be especially dangerous for very young children and people 65 and older. Elderly people account for about 90 percent of all flu-related deaths.
Simply stated: The flu shot saves lives, the CDC says.
Yet a growing number of doctors, scientists and citizen organizations, such as Safe Minds, the Coalition for Mercury-Free Drugs and Moms Against Mercury, say mercury in flu shots has not been proved to be safe and can be linked to neurological disorders and other serious problems. They push for mercury-free shots that are available in limited quantities but that few know about.
"Mercury causes tremendous damage to the brain," said Paul King, scientific adviser for the Coalition for Mercury-Free Drugs.
Mercury is among the most toxic heavy metals and is known to poison the central nervous system, liver, gastrointestinal tract and other systems in the body.
About 80 percent of all flu shots distributed in the United States contain a mercury-based preservative called thimerosal. Thimerosal consists of 49.6 percent ethyl mercury, an anti-bacterial, anti-fungal that allows manufacturers to sell the vaccine in large, multi-dose containers without fear of contamination.
The Environmental Protection Agency and federal Food and Drug Administration have not set an exposure limit for ethyl mercury.
The federal agencies have, however, set exposure limits for another organic and closely related form of mercury, methyl mercury — the type that comes from coal-fired power plants and is found in fish. They use that standard when estimating the safety of ethyl mercury.
Doctors and scientists debate the differences of the two forms in terms of how they affect the brain and body, but all agree: Both are toxins.
A typical 0.5 milliliter flu shot contains 25 micrograms — or 50,000 parts per billion — of mercury.
The EPA classifies a liquid with 200 parts per billion of mercury as hazardous waste. The limit for drinking water is 2 parts per billion.
Using the standards set for methyl mercury consumption — the kind that's in fish — an average 130-pound person getting the flu shot would exceed the daily limit by more than four times. A 22-pound baby would get more than 25 times the amount of mercury considered safe. And doctors are recommending that many babies and children get two flu shots this season.
A material safety data sheet from Eli Lilly and Co., which no longer makes a flu vaccine, says effects of exposure to thimerosal may include "fetal changes, decreased offspring survival and lung tissue changes. ... Exposure in utero and in children may cause mild to severe mental retardation and mild to severe motor coordination impairment."
It does not state at what levels of exposure these consequences could occur.
The CDC and National Institutes of Health have commissioned a number of studies looking at vaccine safety and any links vaccines might have with autism. In 2001 the Institute of Medicine reported that the evidence was inadequate to say whether thimerosal caused autism or other disorders. The issue warranted further investigation, the report stated.
Several other studies followed. In 2004, the Institute of Medicine reported that it couldn't find a causal relationship between thimerosal-containing vaccines and autism.
This September, another study published in the New England Journal of Medicine was unable to prove a causal relationship between early exposure to thimerosal and neuropsychological outcomes in children ages 7 to 10. It did not address possible links with autism.
Amid all the uncertainty, and considering that mercury is a known neurotoxin, several states, such as California, Illinois and New York, have banned thimerosal in vaccines — including the flu shot — given to young children and pregnant women.
Yet every day, in grocery stores, fast-food restaurants, pharmacies, at work and elsewhere, people are bombarded with the message to "Shoo the flu" and are repeatedly told "the best way to beat the flu is to get a flu shot."
Nothing is ever mentioned about thimerosal.
Nothing is ever said about the manufacturers' warnings for pregnant women.
In late October the American College of Obstetricians and Gynecologists reminded all pregnant women to get the flu shot.
Yet the country's largest maker of the flu vaccine, Sanofi Pasteur, in its own literature distributed in package inserts with the vaccine, specifically states:
"Animal reproduction studies have not been conducted with Influenza Virus Vaccine. It is also not known whether Influenza Virus Vaccine can cause fetal harm when administered to a pregnant woman or can affect reproduction capacity. Influenza Virus Vaccine should be given to a pregnant woman only if clearly needed."
Other flu vaccine makers include similar warnings in package inserts for both types of flu shots.
Novartis, maker of Fluzone, goes on to instruct that the "clinical judgment of the attending physician should prevail at all times in determining whether to administer the vaccine to a pregnant woman."
Yet physicians aren't present at most flu clinics. So, many, such as Aurora Health Care's Visiting Nurse Association, rely on information from the federal government and medical associations.
"The CDC recommends all pregnant women get them," said Lisa Taylor, a registered nurse and clinical coordinator for Aurora Health Care's Shoo the Flu program, which will vaccinate an estimated 90,000 people around southeastern Wisconsin this season.
The CDC cites one study supporting its claim that the vaccination is safe for pregnant women — a 1973 study designed primarily to look at tumors in children up to 1 year old whose mothers received a polio vaccination. It included a sentence stating that one child of more than 2,000 mothers vaccinated with the flu vaccine had a spinal cord tumor.
"It's ridiculous," said David Ayoub, a physician and medical director of Springfield, Ill.-based Prairie Collaborative for Immunization Safety, a group concerned about mercury in vaccinations. "It's a big, big deception.
"Half the kids could have died, but the study never would have shown that because they were specifically looking for tumors," said Ayoub, co-author of "Influenza Vaccination During Pregnancy: A Critical Assessment of the Recommendations of the Advisory Committee on Immunization Practices," published in the Journal of American Physicians and Surgeons in 2006.
Still the CDC defends the study, calling it "relevant" and says other studies also demonstrate the vaccine's safety during pregnancy.
Vaccine manufacturers such as Sanofi Pasteur, MedImmune and Novartis say they're ramping up production of thimerosal-free vaccines but don't have capacity to convert all the flu shots immediately.
Protect yourself
Read the labels and materials that accompany the flu shot
Ask for a preservative-free flu shot
Consult with your physician if you have concerns
To report an adverse reaction to the flu shot, file a report at Vaccine Adverse Event Reporting System (vaers.hhs.gov) or call 800-822-7967
A typical flu shot contains 25 micrograms — or 50,000 parts per billion — of mercury.
The EPA classifies a liquid with 200 parts per billion of mercury as hazardous waste. The limit for drinking water is 2 parts per billion.