NYTimes: Why the Flu Vaccine Fizzled

四月 20, 2008

Published: April 20, 2008

Anyone who dutifully got a flu vaccination this year only to come down with a serious fever, chills or cough had plenty of company. An analysis issued last week by the Centers for Disease Control and Prevention estimated that this year’s vaccine formulation was only 44 percent effective. That feeble performance, along with the virulence of one of the strains, made the flu season much worse than the previous three.

Not all of the news is bad. In a separate report, scientists tracked the previously mystifying origins and pathways of influenza viruses. Such information should help them make better vaccines.

What makes flu so hard to prevent is that the virus changes its molecular structure from year to year. Each year, experts try to guess which strains found anywhere in the world are apt to circulate in this country in the next flu season. They then formulate a vaccine to protect against those strains.

When they guess right, as is usually the case, the vaccine can be 70 to 90 percent effective in healthy adults. When they guess wrong, as happened this year, the mismatch leaves many recipients vulnerable.

This year’s vaccine was designed to protect against two strains of influenza A and one strain of influenza B. Based on an analysis in central Wisconsin, the vaccine proved 58 percent effective against the predominant A strain but totally ineffective against the B strain.

In research that could improve the likelihood of picking the right strains, an international team led by British scientists has documented — through molecular and genetic analysis — how seasonal flu strains evolve and sweep around the world. It turns out that new flu strains emerge in several countries in East and Southeast Asia, and are then carried by travelers to Europe and North America some six to nine months later. Several months after that they reach South America, where they die out. Then the whole process starts over.

Although scientists knew generally that influenza strains often emerge from in and around China, the new research expands the area that bears watching and surely bolsters the case for greatly enhanced surveillance in Asia. With any luck, that would lead to better and earlier identification of the strains that will be circulating — the key to making an effective vaccine.



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