CDC: Flu vaccine's spotty strength no excuse to skip shot

Overall effectiveness against the most widely circulating strain was 47%, but the rate dropped to 9% for older adults, the CDC says.

By — Posted March 11, 2013

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Neither the flu vaccine nor his expertise in influenza could keep Pascal James Imperato, MD, MPH, from catching the virus this season.

“I came down with the worst case of flu, [and] it lingered for a month,” said Dr. Imperato, who was immunized in November 2012 but became ill in January. “I had chills to a severity I never had in my life, and I worked in Africa for six years and got malaria a few times,” said Dr. Imperato, dean of the School of Public Health at SUNY Downstate Medical Center in Brooklyn, N.Y.

Dr. Imperato's case is one example of how this season's flu vaccine offered relatively low levels of protection for adults 65 and older. Overall flu vaccine effectiveness against the most widely circulating and most aggressive strain, influenza A(H3N2), was 47%. That's according to preliminary data from the Centers for Disease Control and Prevention published in the Feb. 22 Morbidity and Mortality Weekly Report. Among adults 65 and older, however, effectiveness against that strain was only 9%, the CDC report said.

That's the lowest flu vaccine efficacy the CDC has seen, said Alicia Fry, MD, MPH, a medical epidemiologist in the agency's influenza division. But she noted that the CDC only recently began reporting specific vaccine effectiveness for the different circulating virus subtypes.

There is no clear reason why this season's immunization offered such poor protection for older adults, Dr. Fry said. One contributing factor probably is that older adults tend to have slower immune responses to vaccines than do younger people, which means that even after immunization, the elderly often can remain susceptible to the virus, she said.

Another key factor could be that manufacturers stopped distributing intramuscular whole-virus flu vaccine in the U.S. in about 2001 and instead offer only split-virus immunization, said Dr. Imperato, a former New York City health commissioner. He said the whole-virus vaccine is believed to offer greater protection against circulating influenza strains because it contains the entire virus particle. In contrast, the split-virus immunization contains only surface antigens of the virus. However, the whole virus vaccine was withdrawn because of concerns regarding the number of patients who complained of soreness and other reactions.

“The question then is, if the flu vaccine is so weak in stimulating antibodies, is it worthwhile to get it?” Dr. Imperato said. He and the CDC said the answer to the question was yes.

Flu seasons are unpredictable and can be severe, as indicated by CDC data on influenza mortalities. Between 1976 and 2006, there were an estimated 3,000 to 49,000 flu-associated deaths each year, the agency said. This season, there have been 10,227 laboratory-confirmed influenza-related hospitalizations since Oct. 1, 2012, and 81 pediatric deaths due to flu, according to the latest CDC figures from the week ending Feb. 23.

Vaccine still the best tool

Although the flu vaccine is imperfect, it is the best tool available to prevent transmission of influenza, medical experts said. The CDC already is preparing how it will get that message out to older adults before the 2013-14 flu season begins, in light of the widespread media attention that has been given to the latest vaccine's low efficacy.

“We are concerned that this news about vaccine effectiveness might discourage some older adults from getting vaccinated” next season, said Kristine Sheedy, PhD, director of communication for the CDC's National Center for Immunization and Respiratory Diseases.

The agency probably will partner with organizations such as the National Council on Aging to help disseminate their message on the importance of flu vaccine to older adults, Sheedy said. The CDC plans to produce informational pieces and participate in radio interviews about the importance of the vaccine in markets where large elderly populations reside.

2012-13 flu shots were only 9% effective in protecting adults 65 and older against the most aggressive flu strain.

Sheedy encouraged primary care physicians and their staffs to urge patients to get the flu vaccine. “Doctors are opinion leaders, and we know a recommendation from them is the most impactful thing.”

She recommended that doctors tell patients, “This vaccine is not what we want it to be, but it's the best way we can protect against flu.”

To help enhance older patients' response to the flu vaccine, Damon B. Raskin, MD, an internist in Pacific Palisades, Calif., offers adults 65 and older Sanofi Pasteur's Fluzone High-Dose, which he said is formulated to provide a strong immune response in older adults compared with traditional flu vaccines. Researchers are studying the impact of this vaccine on older adults' immunity to influenza.

Next season, Dr. Raskin plans to focus on educating his older patients on the facts about flu and influenza vaccine. He plans to tell them, “Just because something wasn't effective one year doesn't mean it won't have more efficacy the next year.” And if that doesn't sell patients on the vaccine, he will assure them, “Some protection is better than no protection.”

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External links

“Interim Adjusted Estimates of Seasonal Influenza Vaccine Effectiveness — United States, February 2013,” Morbidity and Mortality Weekly Report, Feb. 22 (link)

“Situation Update: Summary of Weekly FluView,” Centers for Disease Control and Prevention (link)

“FluView,” Centers for Disease Control and Prevention, weekly flu data (link)

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