An initial priming shot given in advance of a booster shot may be an effective way to protect people against bird flu, researchers say in a presentation at the annual meeting of the Infectious Diseases Society of America.
The findings help address a major question facing public health officials: How to protect against a possible pandemic caused by a virus whose precise viral make-up won't be known until it has already become a threat?
The team from the University of Rochester Medical Center is addressing the question by taking advantage of a small group of people in Rochester who were among the first Americans to be vaccinated against bird flu when the disease first became a human threat in Hong Kong back in 1997 and 1998.
Shortly after the Hong Kong threat, the National Institute of Allergy and Infectious Diseases funded a study in Rochester of an experimental vaccine designed against that form of bird flu. Last year scientists turned to the same group of volunteers, who represent a unique pool of knowledge about bird flu, in a study to determine the effects of giving a booster shot years after a person was originally immunized.
Officials were able to track down 37 people who agreed to take part. Each had received two shots as part of the vaccine study in 1998 against the form of the virus that had emerged in Hong Kong. Earlier this year each was again vaccinated with another shot targeting a different form of bird flu, the variant that swept through Vietnam in 2004 and 2005. Their immune response to the second shot was compared to the response in people who received shots for the first time in 2005. More than twice as many people who also received the shot in 1998 developed a protective antibody response against bird flu compared to people who had never been immunized against bird flu previously.
"We studied a relatively small group, so that certainly, this issue needs to be studied more thoroughly in a larger group of people," said John J. Treanor, M.D., professor of medicine and director of Rochester's Vaccine and Treatment Evaluation Unit. "If the findings hold up, then it might open up a number of options beneficial for planning. One might consider giving a priming shot to members of the community who would be a central part of the response if a pandemic were to occur, such as health care workers. You'd have people who were prepared as much as possible in advance."
The work is being presented at IDSA by research fellow Nega Ali Goji, M.D., who did the study with Treanor
The work addresses one of the features of bird flu that makes a potential pandemic so hard to fight: Like human flu viruses, bird flu mutates constantly, and by the time a vaccine has been produced to protect against one form of bird flu, it's very possible that another form, requiring a different vaccine, will have emerged that can move from person to person.
The results of the new study are similar to what doctors already know about giving "regular" flu shots. Every year millions of adults get an updated flu shot every year – one shot is enough, because their immune systems "remember" previous forms of the flu and help make the new shot each year effective. But small children who have never seen the flu before typically need two shots, a primer and a booster. The results from the new study indicate that, like small children who receive a regular flu shot, adults who have never encountered bird flu would benefit from a booster shot.
The two vaccines used in the study target viruses belonging to different "clades" or viral families. Both are H5N1 bird flu viruses, but the Hong Kong strain from 1997 belongs to clade 3, while the Vietnam strain from 2004 belongs to clade 1. Goji and Treanor found that the shot targeting clade 3 helps the body maximize the immunization against a virus in a different clade, clade 1. In other words, using the vaccines that are available now might help improve the response to the vaccines developed for a future strain of bird flu.
The work was possible thanks to the availability of volunteers in Rochester who took part in the nation's first U.S. human bird flu study, back in 1998, at the University of Rochester Medical Center. At the University's VTEU, thanks to funding from NIAID, more than 450 people have taken part in studies of bird flu vaccine, more than nearly any city in the world.
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