HOUSTON — A recent Rice University study predicts the flu vaccine for fall 2018 — a new H3N2 formulation for the first time since 2015 — will likely have the same reduced efficacy against the dominant circulating strain of influenza A as the vaccine given in 2016 and 2017 due to viral mutations related to vaccine production in eggs.

The Rice method, known as pEpitope (pronounced PEE-epih-tope), was invented more than 10 years ago, as a fast, inexpensive way of gauging the effectiveness of proposed flu vaccine formulations. The latest pEpitope study suggests pEpitope is a more accurate predictor of vaccine efficacy than long-relied-upon ferret tests, particularly for data gathered in the past decade. The pEpitope method accounts for 77% of what impacts efficacy of the vaccine in humans. pEpitope is a computational method that measures critical differences in the genetic sequences of flu strains. In the new study, the method accurately predicted vaccine efficacy rates for more than 40 years of flu records. These included the past two flu seasons in which vaccines offered only limited protection against the most widely circulating strain of influenza A.

“The vaccine has been changed for 2018-19, but unfortunately it still contains two critical mutations that arise from the egg-based vaccine production process,” said Michael Deem, Rice’s John W. Cox professor in biochemical and genetic engineering and professor of physics and astronomy. “Our study found that these same mutations halved the efficacy of flu vaccines in the past two seasons, and we expect they will lower the efficacy of the next vaccine in a similar manner.”

Full efficacy data for the 2017-2018 flu season are still being compiled, but pEpitope has predicted it will be around 19% against H3N2, the type of influenza A that infected most people in the U.S. in each of the past two years. The Food and Drug Administration chose the same vaccine formulation in 2017 and 2016, in part because the dominant circulating strain stayed the same. In 2016, the vaccine had an efficacy of 20%, almost identical to the efficacy of 19% predicted by pEpitope.

Efficacy is the measure of how effective a vaccine is at protecting the overall population. For instance, a 20% efficacy means that in a population, 20% fewer vaccinated people will get the flu compared to the unvaccinated people.