A Cautionary Tale  pg. 4

Once the group identifies three dominant viral strains, pharmaceutical companies estimate the number of vaccines needed around the world and grow them up in chicken eggs, a time-consuming technique that has been used since the 1940s.

Reverse genetics

Speaking from Hong Kong, where he is part of the WHO surveillance team, Robert Webster, Ph.D., an infectious disease expert at St. Jude Children’s Research Hospital in Memphis, claims that they knew Fujian-A was in the human population as early as February 2003, but they couldn’t grow it up in time for a vaccine. Had they been able to use a technique known as “reverse genetics,” he insists, Fujian-A would not have wreaked such havoc.

The current technique for developing a vaccine requires six months, and tens of millions of eggs. Scientists produce a “viral seed strain” by reassorting two currently circulating viruses. With reverse genetics, scientists can rapidly engineer the seed strain in the laboratory by picking and choosing the H and N genes they want. In this way, they can custom design a vaccine that will be safe for humans, but which will also generate an immune response. The virus still must be grown up in eggs to produce a vaccine, but the process can be completed in weeks instead of months.

“We have the technique for reverse genetics,” Webster says, “and it could have been used this year, but it’s not an approved method yet. We have to get approval for using that technique to generate vaccines quickly.” The flu vaccine shortage that occurred this winter “is just the tip of the iceberg,” he says. For example, a strain of avian flu even more virulent than the one that spread through Asia this winter could appear in the United States and cause more illness and death than the Fujian-A strain did. He adds, “If we get one of the new strains we’re seeing in animals in Hong Kong, and if you think we’re going to have plenty of vaccine in the face of pandemic, think again.”

Part of the problem, says Marie Griffin, M.D., a pharmacoepidemiologist and professor of Preventive Medicine at Vanderbilt, is that the burden of disease from influenza has, historically, been under-appreciated. The past three or four flu seasons have been mild, so Americans didn’t rush out to get a flu vaccine, and manufacturers threw away millions of excess doses last year. Each year influenza causes around 40,000 excess deaths, mostly in people over the age of 65, many of whom have other chronic illnesses. However, annually around 20 percent to 40 percent of children, who may be immunologically “naïve” to a new flu strain, also come down with influenza.

“What tips the balance towards us recommending that children get vaccinated is that some of those kids have severe consequences from flu,” Griffin says. “What we’re learning, or maybe learning again, is that there are quite a few kids under the age of two who end up getting hospitalized for influenza, which is a bad outcome even if few of those kids die.”

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