More than 10 million older Americans traveled last year, often in lousy weather, to stand in long lines and get poked in the arm with a flu shot. They made the trip in response to recommendations by the federal government that gave priority for flu vaccines to the elderly and the ailing. This, it turns out, is probably a bad idea. A Harvard study published last week adds to mounting evidence that the best way to ward off the flu's ravages is to target transmission (meaning a disease's main carriers, which in this case are kids) rather than risk (meaning the population at risk of death or serious illness, which with the flu is the old, the ailing, and infants). All signs are that giving children quick, painless nasal-spray vaccines while they're already gathered at school could spare the elderly from standing in long lines for flu shots—and better protect them and everyone else.
The 60,000 deaths in the United States from ordinary flu each year are reason enough to consider changing the country's approach to flu vaccination. Fighting the flu efficiently is all the more important in light of growing fears about an avian flu pandemic. Last week, researchers broke the genetic code of the killer 1918 Spanish flu epidemic and showed that it in some ways resembles the current bird-flu virus stalking Asia. If, as many experts fear, today's avian flu makes a jump to human-to-human transmission like the Spanish flu did, quickly dosing key populations with vaccines or antivirals will be crucial to preventing or containing a pandemic. Yet as anyone who queued up last year for a flu shot knows—and as the draft of the Bush administration's plan for controlling a flu pandemic that leaked last week makes doubly clear—the current system can't handle the job.
Here's why it makes sense to set up a better system based on vaccinating kids instead of the sick and the old. Because the human immune system weakens with age, only 28 percent of elderly people who get vaccinated develop immunity. The low rate of protection means that 84 percent of all elderly (the 72 percent whose vaccinations don't take, along with those who don't get vaccinated) remain prey to a flu virus that runs otherwise largely unchecked.
This vulnerability, combined with the aging of the population, has caused the nation's overall flu death rate to rise 400 percent even as we vaccinate more of the elderly. (Click here for more numbers.) The Harvard study published last week, meanwhile, demonstrates why it makes more sense to vaccinate kids. The researchers confirmed that the flu spreads primarily via toddlers and school children, whose immature immune systems are easily infected and who have lousy hygiene. Kids often don't wipe their noses, wash their hands, or cover their mouths when they sneeze or cough, and they touch everything. That's why they catch the flu twice as often as and much earlier in the season than older people do. For an airborne virus, kids are the conduit of choice.
Fortunately, though, kids are also the conduit most easily blocked. Their immune systems respond wonderfully to flu vaccine. A whopping 90 percent are successfully immunized by a flu shot, compared to the 28 percent figure for the elderly and 60 percent for middle-aged adults. Kids' 90 percent success rate has been used to set up viral roadblocks high and wide enough to increase protection for whole populations. In the late 1960s, for instance, University of Michigan researchers vaccinated 85 percent of the schoolchildren in Tecumseh, Mich. The program reduced flu cases by two-thirds. In the late 1990s, a Baylor College of Medicine study vaccinated just 25 percent of 18-month to 18-year-olds in Temple, Texas, every year for three years. Adult flu cases dropped 8 percent to 18 percent.
Then there's Japan. Following a devastating 1957 epidemic, Japan in 1963 established mandatory childhood flu immunization. By 1970 the country was vaccinating 50 percent to 85 percent of schoolchildren annually. Between that year and 1987, flu-related deaths fell 40 percent, saving 40,000 lives a year. This drop occurred even though Japan's elderly population almost doubled during that period. When the country phased out mandatory vaccinations for kids beginning in 1987, flu deaths in every age group started rising and have continued doing so ever since.
Computer models developed by Emory University's Ira Longini and Elizabeth Halloran suggest the United States could follow Japan's example. These models show that as child-age vaccination rates pass 50 percent, a community increasingly gains overall resistance to disease—what epidemiologists call "herd health"—which protects even those most at risk. Specifically, vaccinating 30 percent of preschool and schoolchildren would reduce a community's chance of flu epidemic from 90 percent to 65 percent. Vaccinating 50 percent of kids would cut the chance to 36 percent. And vaccinating 70 percent of them would shrink the risk of epidemic to 4 percent. Any of those scenarios would prevent more elderly deaths than giving flu shots to 90 percent of seniors.
Vaccinating between 50 percent and 70 percent of kids would be well within reach if the United States were to set up a free, voluntary, and national program of nasal-spray flu vaccines for children between the ages of 6 months and 17 years. Is such an effort likely? At the moment, no federal or state plan calls for so much as a trial. On the encouraging side, the Centers for Disease Control will co-sponsor a conference later this month (titled "Universal Flu Vaccine: Are We Ready?") to review herd-health research. But despite the recent Harvard study and others, CDC officials so far consider the evidence for child vaccination too thin to justify even a test program. They worry that widespread child vaccines will fail to protect the rest of the population, and they say they're not sure the United States could secure enough vaccines.
The latter concern is legitimate in the short term. The main supplier of nasal spray vaccines, Medimmune, now makes only a couple million doses a year. They require frozen storage, which makes distribution tricky. But a refrigerator-friendly version of the vaccine should be out by 2007, vastly simplifying storage and transport. And Medimmune plans to expand production to tens of millions of doses within the next three years to five years. It seems a safe bet that if the United States wanted to buy, say, 50 million doses in a year or two, some company would make them available for sale. As an alternative or in addition to nasal sprays, a child vaccination program could also use some of the 65 million syringe doses presently used each year. Fifty million doses would vaccinate 72 percent of the nation's 69 million children, cutting the chances of a national flu epidemic to the single digits—saving up to 50,000 lives a year, tens of millions of lost work and school days, and great piles of money.
Establishing a national child-based flu-vaccination system would also create an asset we lack—a simple, familiar, and effective way to distribute and administer vaccines or antivirals if a flu pandemic strikes. The recent analysis of the 1918 flu's genetic code greatly increases virologists' chances of developing a vaccine or antiviral drug that could check a pandemic arising from the avian flu now brewing in Asia. But because bird flu spreads quickly, with people contagious before they're symptomatic, a pandemic can be stopped only if public health officials can quickly get the drugs to key parts of the population. Our present ad hoc system can't do this. A school-based system could.
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