April 2, 2001 -- People with egg allergies have more to watch for than what they eat. Because flu vaccines made in the U.S. are "grown" in chicken eggs, people who are allergic to eggs are advised to skip the annual flu shot. But now researchers in Europe have developed a new method for making the flu vaccine -- an egg-free method that may make it possible to vaccinate people allergic to eggs, while also decreasing the likelihood of vaccine shortages, such as the one that recently plagued the U.S.
The new method is based on growing the vaccine under "protein-free" conditions by using kidney cells obtained from the African green monkey. This method reduces the chances of an allergic reaction because it is the egg proteins that cause the reactions.
The new manufacturing method may represent the best approach discovered so far for making the flu vaccine, according to Otfried Kistner, PhD, who described the method Monday at the national meeting of the American Chemical Society in San Diego.
Kistner is director of the research project for Baxter Hyland Immuno in Austria, the company that developed the manufacturing method.
Besides eliminating the potential for an allergic reaction by using something other than eggs, the manufacturing method also eliminated the need for a preservative that also has been linked to health risks, including allergic reactions, Kistner explains. The mercury-based preservative thimerosal is often used in protein-based vaccines to kill bacteria.
"The point is that we have complete protein-free conditions," Kistner tells WebMD.
Another advantage to the new method is that it may speed up production of the flu vaccine during an outbreak, Kistner says.
The dependency on eggs to grow vaccines may delay the production of vaccines during an outbreak because vaccine makers may have difficulty gathering eggs or modifying the inactive virus used in the vaccine to grow in eggs, Kistner explains.
The new method, Kistner tells WebMD, does not require modifying the virus since the inactive version will grow without modification in the monkey kidney cells. In addition, unlike eggs, the kidney cells can be stored for use in an emergency, he says.
Although other manufacturers are testing egg-free vaccines, Kistner says that this approach is especially promising because the monkey cells used to develop this vaccine already have been approved in Europe and the U.S. for the production of other vaccines.
In fact, he tells WebMD, the cells used by researchers have been used for more than 50 years to produce a Polio vaccine.
Some experts say the most significant advantage to the new production method may be its ability to speed up production rather than its elimination of the egg protein.
"The egg allergy really has not raised a problem," says Stanley Goldstein, MD, a spokesman for the American Academy of Allergy, Asthma, and Immunology and director of the Allergy and Asthma Care Institute in Long Island, N.Y.
This is because the egg allergy is more common in children than in adults and is rarely present in children with weak immune systems -- a group that would be top candidates for the flu vaccine -- he tells WebMD. Children also often outgrow their egg allergy by the time they become adults, Goldstein says.
Still, the vaccine may offer other advantages, Kistner says.
According to Kistner, the experimental vaccine may prove safer -- at least in the case of older adults. In a series of clinical trials involving more than 2,500 volunteers, the new vaccine caused significantly fewer adverse effects than the conventional vaccine among people aged 60 and older, Kistner says.
In the younger age groups, there were no significant differences in the rate of adverse events. The most common side effects were typically mild local reactions at the injection site, such as reddening of the skin and swelling.
Nevertheless, it may be sometime before any American benefits.
Although European authorities are expected to approve the vaccine later this year, clinical trials have yet to begin in the U.S.
"We plan to start those clinical trials next year," Kistner tells WebMD.
If all goes according to plan, Kistner says the new vaccine should then be available in the U.S. just in time for the 2004 or 2005 flu season.