Large Study Reaffirms H1N1, Seasonal Flu Vaccine Safety

Release Date: July 5, 2011 | By Emily Paulsen, Contributing Writer
Research Source: American Journal of Preventive Medicine


  • Both the H1N1 and seasonal influenza vaccines are safe for patients, a new Harvard study shows.
  • The CDC monitors flu vaccine safety using data from millions of U.S. children and adults.
  • Unlike the 1976 swine flu vaccine, newer flu vaccines do not put patients at risk for Guillain-Barre syndrome or Bell’s palsy.
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Back in spring 2009, the H1N1 influenza virus crossed the U.S. border and raised concerns that it might cause a full-scale epidemic in the fall. The Food and Drug Administration worked with other Health and Human Services agencies and vaccine manufacturers to quickly develop, license and distribute a vaccine to protect the public from this particularly virulent strain of the flu.

However, alongside the public’s concern about H1N1 were also fears that the rapid vaccine development would lead to unanticipated problems similar to the increased risk of Guillain-Barré syndrome that occurred with the 1976 swine flu vaccine.

A new study shows that those fears were unsubstantiated and reaffirms the safety of the seasonal flu and H1N1 influenza vaccines.

“In the 2009-2010 season, when everyone was concerned about H1N1 because it was so new,” data analysis showed no increased risk for specific side effects, said Grace M. Lee, M.D., lead researcher. “This is very reassuring.”

Lee is an assistant professor of population medicine and pediatrics at Harvard Pilgrim Health Care and Harvard Medical School. The study, which relied on data from the Centers for Disease Control’s Vaccine Safety Datalink Project (VSD), appears online and in the August issue of the American Journal of Preventive Medicine.

At the start of the 2009-2010 flu season, the VSD Project began tracking data on a near-real time basis from eight medical organizations that together give care to 9.2 million children and adults. Each week, the organizations provided combined data for all immunizations, hospital admissions, emergency visits, outpatient encounters and diagnoses. Researchers then looked at the incidence of adverse events potentially associated with immunization, including Guillain-Barré syndrome, seizures, Bell’s palsy, other neurologic conditions and allergic reactions to detect any possible problem early enough to prevent widespread occurrence.

The analysis found no elevated risk for any adverse event, including Guillain-Barré syndrome, a condition that causes varying degrees of muscle weakness.

In the course of the study, researchers found one “safety signal,” an elevated incidence following the H1N1 vaccine of Bell’s palsy, a condition in which the muscles on one side of the face become paralyzed and which often resolves over time. When researchers dug deeper and adjusted for the fact that Bell’s palsy generally is more common during flu season  — late fall through winter — they found no association between the H1N1 vaccine and an increased incidence of Bell’s palsy.

Jon Abramson, M.D., chair of the pediatrics department at Wake Forest Baptist medical center and a member of the World Health Organization’s Strategic Advisory Group of Experts on Immunization, said he hopes this study will further convince the public of the safety and benefits of the flu vaccine. While flu immunization rates hover just over 40 percent — much lower than the 90-plus percent he said he would like to see — rates have increased in recent years.

“We’ve been using the influenza vaccine for now close to 50 years and there’s a tremendous amount of data that say it’s safe,” he said. However, Abramson said that ongoing monitoring systems such as VDS are critical to detecting or preventing situations such as the increased incidence of Guillain-Barré syndrome associated with the swine flu vaccine.

“Every year they’re changing the virus strain and every year there’s some chance that a strain will cause a specific problem, like what happened in 1976,” Abramson said. He added that, except for what happened in 1976, studies indicate that Guillain-Barré syndrome occurs more often because of an infection by the flu virus itself, rather than from getting the vaccine. “The risk-benefit ratio is clearly in favor of the vaccine.”

TERMS OF USE: This story is protected by copyright. When reproducing any material, including interview excerpts, attribution to the Health Behavior News Service, part of the Center for Advancing Health, is required.

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For More Information:

Reach the Health Behavior News Service, part of the Center for Advancing Health, at (202) 387-2829 or

American Journal of Preventive Medicine: Contact the editorial office at (858) 534-9340 or

Lee GM, et al. H1N1 and seasonal influenza vaccine safety in the Vaccine Safety Datalink Project. Am J Prev Med 41(2), 2011.

Tags for this article:
Immunizations/Vaccinations   Lifestyle and Prevention  

Comments on this article
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Concerned says
July 5, 2011 at 12:33 AM

All this proves is big pharma is doing everything they can to save the millions of dollars in revenues they make off this vaccine. The big questions aren't answered in this

Scientific says
July 6, 2011 at 11:50 PM

Obviously we'll watch all the conspiracy theorists and vaccine haters dash off unfounded accusations here, but this safety study is well in line with preliminary study data for H1N1 vaccine production. The Institute of Medicine and WHO have concluded that influenza vaccines, including the novel H1N1 vaccine, both Hemagglutinin and LAIV forms are safe and effective at saving lives.

Realist says
July 12, 2011 at 11:42 AM

Not much profit is made on vaccines - it's the other pharmaceuticals that are bringing in the money. The question of safety in using the flu vaccine is clearly outlined in this article. No need to go searching for another meaning.

Astro says
July 13, 2011 at 12:30 AM

We'll, we all know the hazards of cigarettes and alcohols, but why the government can't stop it? The REAL and only reason behind is MONEY! Government agencies that supposedly protectors of its citizens are now protectors of BIG Companies. So true with Giant Pharma Companies. IT'S ALL ABOUT MONEY!! They don't care if YOU DIE as long as they have their MONEY!

Need more data says
July 14, 2011 at 6:35 PM

Adjusting for seasonality did not have

Need more data says
July 14, 2011 at 6:36 PM

Adjusting for seasonality did not have no association with Bell's Palsy. It had an odds ratio of 1.26 (95 percent confidence interval, 0.97 to 1.63). That was considered

Need more data says
July 14, 2011 at 6:38 PM

One more try....

Adjusting for seasonality did not have no association with Bell's Palsy. It had an odds ratio of 1.26 (95 percent confidence interval, 0.97 to 1.63). That was considered borderline in the study below, for example, and warranting further study.

Also the numbers looked at in the flu vaccine study are too low to see signals for GBS at all, aren't they?

And what would be truly helpful for consumers would be to compare outcomes for both GBS and BP.

Just search for 'vaccine industry profits.' They are lucrative and the industry is not secretive about that. Their own trade publications are an excellent resource. Liability is limited by the government and public funding for research for the industry is significant.