The Food and Drug Administration in late 2009 licensed Fluzone High-Dose, made by Sanofi Pasteur in Swiftwater, Pa., for use in people 65 and older. There was limited research on other groups, such as people with HIV.
The elderly and people with compromised immune systems account for the vast majority of the thousands of deaths from seasonal influenza. They get sicker and are more likely to experience serious complications. They also produce a weaker response to standard vaccine, making them more likely to catch the flu.
"A higher dose of vaccine is more immunogenic," Tebas said. The stronger immune response found in people with HIV, he said, was similar to that produced by older people with Fluzone High-Dose. It also matched the response in healthy younger adults to the standard vaccines.
Researchers around the country have been looking for ways to give better protection from the flu to people with HIV and those with medical conditions - cancer, rheumatoid arthritis, renal failure - whose treatment suppresses the immune system.
Lacking other options, hospitals occasionally give double doses of standard flu vaccine to patients with very compromised immune systems, said Donna Curtis, an infectious-diseases doctor at Children's Hospital Colorado who is starting her own study of Fluzone High-Dose in young people with HIV and other disorders.
The Philadelphia study was led by Noah McKittrick, then at Penn and now at Thomas Jefferson University, and involved researchers at Penn and at Drexel University. They enrolled 190 HIV positive adults at Penn's MacGregor Clinic during the 2010-11 flu season, the first time the high-dose vaccine was available. Half were randomly assigned to get a high dose; the other half got the standard version of Fluzone.
The high-dose group produced more antibodies than the standard group against all three influenza strains in that season's vaccine, although the increase was statistically significant for only two of them.
Both groups had started the season with relatively high levels of protection. The researchers attributed that to the lingering effects of high immunization rates the previous year, which included onetime shots against pandemic flu.
More than 90 percent of participants in the high-dose group produced immune responses considered protective against each of the three strains. No serious adverse events were reported. An increase in minor reactions, such as pain at the injection site, was similar to that seen in the elderly.
One unanswered question is whether high-dose vaccine can produce a strong enough response among sicker patients. Few participants in the study had CD4 counts under 200, a measure of infection-fighting white blood cells that is used to diagnose AIDS, the disease caused by the HIV virus.
The 14 patients in this category who got high-dose vaccine produced a weaker immune response than other patients but it was still better than their counterparts who received a standard dose, the researchers said.
Another question is whether the vaccine will actually prevent the flu. This study, like many others, including those used to win approval of Fluzone High-Dose for the elderly, measured the level of antibodies to protect against the flu - not the flu itself, which would require longer, larger, and costlier studies.
Tebas said the evidence was strong enough that the authors would immediately write the Advisory Committee on Immunization Practices to suggest that it recommend the high-dose vaccine for HIV infected people. He said the team was acting independently of Sanofi Pasteur, which did not fund the study. It was supported by the National Institutes of Health.
A Sanofi spokesman said the company would not comment on the research.
Although the FDA's 2009 approval labeled the vaccine as a product for the elderly, vaccines can also be used "off label" the same way some medicines are prescribed by doctors for purposes not listed on the package insert.
Because of their broad use as a preventive public health measure, vaccines get further scrutiny from the immunization practices committee, a panel of experts that advises the Centers for Disease Control and Prevention on guidance to give clinicians.
It occasionally recommends uses broader than the FDA approved, said Jean Clare Smith, the staff medical officer for the committee. To address a pertussis epidemic, for example, she said the committee recently recommended that the Tdap vaccine be given to women during every pregnancy. But she said the committee needs a compelling reason to go beyond the approval given by CDC's sister agency, the FDA.
Some doctors may begin offering high-dose vaccine to their HIV patients based on the new research but insurance companies are unlikely to cover it without a recommendation from the CDC.
"Obviously, you want something that will be effective," said Ellen Tedaldi, director of Temple University School of Medicine's HIV program, who was not involved with the study. She declined to say whether she would offer the high-dose vaccine to her patients.
"It will be interesting to see how this translates into practice," she said.
Contact Don Sapatkin at 215-854-2617 or firstname.lastname@example.org.