A study conducted by the Centers for Disease Control and Prevention (CDC) from November 2017 to February 2018 estimated the flu vaccine’s effectiveness to be a rather underwhelming 36 percent overall in the United States.
Effectiveness for each of the three individual flu strains included in the vaccine — H3N2, H1N1, and a type B lineage — varies significantly. Against the particularly nasty and widely circulating H3N2 strain responsible for causing about 69 percent of illnesses this season, the vaccine is just 25 percent effective. This value increases to 59 percent, however, among the traditionally highly vulnerable “children aged six months through eight years” demographic. The vaccine also does fairly well against H1N1 and type B with 67 and 42 percent effectiveness, respectively.
When gauging 2017–2018 flu vaccine effectiveness, it is important to consider factors that can influence efficacy drastically in any given year.
Choosing Flu Strains Is A Guessing Game
In February of each year, the World Health Organization (WHO) makes an educated guess based on surveillance and lab and clinical studies about which influenza strains it believes will be prominent in the fall. The Food and Drug Administration (FDA) makes the final call in the United States based on this data, and a vaccine is developed months in advance for a flu season that generally starts in October and runs until May. Flu vaccine effectiveness hovers somewhere between 50 and 60 percent in a year there is a good match between the predicted and actual circulating strains. In years with a poor match, vaccine efficacy can be as little as ten to twelve percent.
Not All Strains Are Created Equal
Some flu strains wreak more havoc than others, and flu seasons prominently featuring the H3N2 strain tend to be markedly worse. The reason for this is not entirely understood, but science is pointing to the vaccine development process itself as the culprit.
A vast majority of flu vaccine synthesized in the U.S. is cultivated in chicken eggs. Live viruses are injected into fertilized hen’s eggs and incubated before the flu strains are harvested, killed or inactivated, and purified for use in vaccinations. During this process, H3N2 appears to undergo more genetic changes than other strains, which results in it becoming more suitable for the chicken egg environment but less likely to elicit the proper immune response when injected into humans.
While there is emerging evidence from the CDC that other flu vaccines on the U.S. market made from dog kidney cells or synthetic insect cells remain closer to the circulating strains, there is much more research needed. Alternative vaccine development procedures have not conclusively proven to result in more effective vaccines and are not nearly as cheap as the established egg method.
Flu Vaccine Effectiveness 2018: Recommendation From The Experts
Even in years with mismatched strain predictions or H3N2 featuring heavily, experts still recommend getting the vaccine due to its low risk and cost. Still, others argue that the flu vaccine, like most vaccines, is not without potential side effects regardless of its efficacy.
Learn more about the Flu Vaccine.
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