Every year, starting around November, influenza virus sweeps across the United States. And every year doctors and public health officials urge citizens to get their influenza vaccine.
For several reasons, influenza is arguably humankind’s most heinous and most burdensome infection. First, the virus kills more people than all other vaccine-preventable diseases combined; as many as 50,000 people succumb to influenza in the United States every year. Second, influenza virus mutates so much from one year to the next that preventing it requires a yearly vaccine; neither immunization nor natural infection the previous year protects against disease the following year. Third, because the Centers for Disease Control and Prevention (CDC) recommends the influenza vaccine for everyone more than 6 months of age, the health system is burdened with immunizing hundreds of millions of people every year. Finally, although the influenza vaccine is the best tool available to prevent the disease, it’s less effective than any other vaccine. Last year’s influenza vaccine is a perfect example.
The 2016-2017 influenza vaccine reduced out-patient visits by only 42 percent and was progressively less effective in older age groups. For children 6 months to 8 years of age, the vaccine reduced the incidence of influenza by 61 percent; for children 9 to 17 years old, by 35 percent; and for adults more than 65 years old, by 25 percent. Although 25 to 61 percent protection is better than 0 percent, the fact remains that most people more than 8 years old who received the influenza vaccine weren’t protected against the disease.
Last year’s influenza vaccine also wasn’t particularly good at preventing severe influenza infections, reducing hospitalizations by 30 percent for those more than 18 years old and 37 percent for those more than 65. Again, a 30 to 37 percent reduction in hospitalizations is better than 0 percent, but the public would be better served by a better vaccine.
A number of explanations have been offered to account for the influenza vaccine’s weaknesses. One is true; one is unlikely; two will surprise you.
(1) The vaccine viruses don’t match the viruses that cause disease.
Several different types of influenza virus cause disease. To determine which ones to include in a yearly vaccine, researchers isolate the strains that are circulating in South America. These strains typically sweep up into the United States and cause yearly epidemics. Sometimes, however, the strains of influenza virus circulating in South America mutate before they enter the United States. Public health officials refer to this as a “bad-match year.” The 2014-2015 influenza season, for example, was a such a year; protection afforded by…