Another example of unfolding science: RotaShield, a vaccine against the leading cause of infant diarrhea, was approved in 1998. When a very rare side effect emerged, the vaccine was pulled in 1999. Two new vaccines were developed and licensed in 2006 (Rotarix and RotaTeq), and those formulations may save hundreds of thousands of lives annually worldwide. Again, more tweaks may be needed over time. In fact, the American Academy of Pediatrics vaccine schedule is constantly changing in small ways—ask any pediatrician who has to keep up—as data filters back about new vaccines against HPV and meningococcus, among others.
Back to flu, which is far more complicated than, say, chicken pox. To begin with, most people who die of the flu aren’t actually tested for it; hospitals and clinics aren’t required to report flu cases to anyone (unless they involve young children); and most severe consequences of the flu are secondary problems like bacterial pneumonia or heart failure, which end up being listed as the cause of death. Thus, the flu’s toll can be estimated only by using complex statistical models. Further, the virus mutates yearly, so the flu’s impact varies hugely year by year and makes longitudinal comparisons impossible. Over the past 30 years, the annual American death toll wandered almost randomly between 3,000 and 50,000.
Now add the following: Vaccine makers have to guess what strains of the flu will predominate, so the vaccine may prevent anywhere from 0 to 50 percent of the flu in a bad-guess year and 70 to 90 percent in a good-guess year. The vaccine works best in school-age children and young adults, and unfortunately it works worst in babies and seniors, who sadly are the ones who get sickest. (In 2003, the CDC began requiring state health department to report child flu deaths and found 153 children died of the flu that season, which is more than any other vaccine-preventable illness.) Even more complicated: The nasal mist vaccine works best in children, but the shot is better for adults.
What about Tamiflu? In the event that a virulent flu pandemic occurred and no vaccine was available, antiviral drugs might be critical. In a key 2009 study during the H1N1 outbreak, stockpiled Tamiflu was given to large groups of contacts of newly-infected Singaporeans and cut the transmission rate by 95 percent. Tamiflu also appears to cut the risk of death in hospitalized flu patients. Critics of Tamiflu allege Roche obscured evidence unfavorable to the drug, but the debate is deep and fascinating. (Roche’s response to them, in my opinion, seemed reasonable.)
Most importantly, what have we learned about flu control? We found that vaccinating the elderly failed to cut hospitalizations; therefore, doctors hypothesized that children are responsible for spreading most flu to older people. In 2010, a large study of elementary-school-based flu vaccine in Bell County, Texas achieved 50 percent vaccination rates of students and protected people of all ages from the flu (the so-called “herd immunity” effect). Similar findings were seen in a Canadian study. Incorporating this information, the CDC recommended in 2010 that all people over 6 months old should be vaccinated. (To guard infants, we now know that vaccinating pregnant women produces immunity in their newborns.) As in chicken pox control, these new flu policies show public health in evolution. In a few years, we will see if this works. In the meantime, the FDA earlier this year approved a new vaccine that includes four flu strains, instead of three, which may bolster effectiveness. It’s another example of science in action.
In the meantime, Americans should learn from the death toll of flu-vaccine skepticism in Japan. It was the only industrialized country to have mandatory universal flu vaccine of children, which helped produce herd immunity, The program fell victim to skeptics and was repealed in 1994. The result? The New England Journal of Medicine reported that flu deaths rose by 40,000 per year—almost as many people as died immediately from the atomic bomb in Hiroshima.
In the end, it’s easy to ascribe sinister motives to flu control efforts, especially if you’re unwilling to tolerate uncertainty. With a slight shift in perspective, however, one can see our evolving flu control programs as a triumph of public health.