The First Flu You Ever Had Affects Your Whole Life

The First Flu

The year you were born might predict how you’ll respond to this year’s flu—and how well you’d fare in a flu pandemic.

The First Flu

A phenomenon known as imprinting might be responsible for an unusual pattern in the ages of people going to the hospital with the flu. Imprinting here refers to how our immune response to the flu is shaped by our medical history.

Specifically, the first flu virus a person catches shapes their immune response to other strains encountered later in life. The strain to which we lose our flu virginity, as it were, affects how we react to all the subsequent strains we meet. “The first strain you meet has a special status,” said James O. Lloyd-Smith, a researcher at the University of California, Los Angeles.

Dr. Dan Jernigan, director of the influenza division of the Centers for Disease Control and Prevention’s National Center for Immunization and Respiratory Diseases, suggested in late January that imprinting might explain why baby boomers are being particularly hard hit this flu season.

Usually the imprinting phenomenon protects us by helping the immune system react more quickly to new virus strains. If the hemagglutinin—a protein on the surface of the virus—is similar to the hemagglutinin encountered in prior strains, then the immune system may produce antibodies to the new virus just upon detecting that protein resemblance.

But the flu changes each year. And one major change in 1968 may help explain why baby boomers are at a disadvantage now.

The problem stems from the strain of flu virus to which those boomers first succumbed. Everyone who is currently at least 50 years old was born before 1968. And the 1968 flu pandemic was the first time in decades that a virus with a particular kind of protein on its surface called H3 spread throughout the United States. That means that anyone who is 50 years of age or older this flu season was born too early to be imprinted with an H3 strain of the virus.

But the H3N2 strain is responsible for many of the flu cases in the United States this year. This year, the typical boomer immune system is relatively less prepared to fight back than those of younger people, who had a chance of being imprinted with an H3 flu strain.

It’s tempting to think that birth year alone could help people make health decisions. For example, if H3 viruses are prevalent in a given year, then people over 50 might have even more of a reason to have the flu vaccine.

But it’s not that simple. Since 1977, both H3 and H1 viruses have circulated. That means it’s anyone’s guess which strain a millennial may have been infected with first. Scientists are looking for a way to detect an imprint within a person’s immune cells, but currently there’s no test to tell which virus a person may have been exposed to first.