The Year in Science: Epidemiology

Problems with the new flu vaccine, and the American robin harbors the West Nile virus.


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New Bird Flu Vaccine Might Not Work in Time

Although confirmed human deaths from bird flu have numbered less than 100 so far, some public-health authorities are worried that it will mutate into a disease that spreads easily and kills millions. So reports in August about a vaccine were welcome news.

The study found that the federally funded vaccine, made by the French drug firm Sanofi-Aventis, is safe and capable of producing antibodies to ward off the current strain of avian flu. Yet there are still plenty of caveats. The new vaccine could arrive too late, not reach enough people, or not defend against the circulating virus for the following reasons:

  • Manufacturing vaccines can take about eight months because they are still produced using 1940s technology. The flu strain is carefully injected into the embryos of chicken eggs, which become tiny incubators for the virus. The virus is then killed with detergents, extracted, and bottled in vials. If a pandemic started tomorrow, millions of people could die before they were inoculated.

  • The three companies that make flu shots are capable of producing only about 150 million doses a year, enough to meet demand for a vaccine against typical yearly flus. Ramping up production to 600 million doses would be a challenge, particularly because the avian flu often kills the chicken embryos. Vaccine manufacturers would need hundreds of millions of eggs.

  • The production cycle is so long that the avian flu could evolve to bypass the new vaccine or any vaccine in production.

Worried international health authorities are encouraging countries to stockpile Tamiflu, an antiviral drug that offers some protection. They are also distributing millions of dollars to encourage the adoption of faster, more modern manufacturing practices, including growing the vaccine in cell cultures rather than in chicken eggs. The drug firm Acambis is trying to go a step further by developing a cell-culture vaccine that after just one injection would prevent every type of flu.

In October two reports described the complete sequence and reconstruction of the 1918 flu virus, which killed an estimated 675,000 Americans and more than 20 million people worldwide. One study found that the 1918 flu probably wasn't a direct mix of bird and human flu strains, as was long suspected, but may instead have been avian flu that managed to adapt to humans over time. The second study found that the strain's extreme virulence, targeting primarily lung tissue, appeared to be linked to changes in four genes. One gene makes the protein that the virus uses to enter cells. The other three make the enzyme needed to copy the virus.

On November 1, President Bush proposed a $7 billion program to fund new methods for producing flu vaccines and to prepare for a pandemic. All these efforts will take time. Meanwhile, the world is waiting, on edge. —Michael Rosenwald 

Mosquito-Borne West Nile Turns Up in an Unsuspected Carrier: the American Robin

Since West Nile virus arrived in the Western Hemisphere in 1999, people have worried each summer about its spread. Although the virus, carried by mosquitoes, has been detected in more than 200 species of birds, crows have been closely monitored as the primary reservoir. This year medical entomologists at the Connecticut Agricultural Experiment Station learned that we may have been watching the wrong bird and the wrong mosquito.

By extracting blood from the stomach of engorged mosquitoes, Theodore Andreadis and his colleagues found that 40 percent of the infected mosquitoes had feasted on the blood of the American robin, a species that can carry the virus without showing symptoms.

A more important finding questions the strategy of disease control for West Nile, which has focused on eradicating a common, easily controlled, ditch-dwelling mosquito. Andreadis found that these mosquitoes rarely bite mammals, so they are not likely to pass the virus on to people.

Salt marsh mosquitoes, on the other hand, pose a greater risk of disease transmission, says Andreadis, because they feed on birds about a third of the time and on mammals more than half the time. And salt marsh mosquitoes are a challenge to control because they breed in vast stretches of pristine marshland along the coast.

Complicating study of the virus even further, a lab study found that an infected mosquito can pass the virus to nearby mosquitoes while they are feeding on an uninfected animal. —Jessa Forte Netting

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