A computer-based tool developed as part of a study by researchers at Rice University in Texas is gauging the anticipated efficacy of this season’s influenza vaccine at 19 percent. The tool, known as pEpitope, is a computational model measuring critical differences in the genetic sequences of circulating strains of influenza virus.

Other flu vaccine efficacy forecasts come from ferret tests and laboratory cell cultures, which the investigators explained have been expensive, time-consuming and unreliable during the past 10 years. In their study, the Rice University researchers noted that ferret-based tests are one third as predictive as the pEpitope test.

“It’s been difficult to get data from ferrets because the ferrets’ immune systems have not recognized the vaccines particularly well over the past 10 years,” said Rice researcher Michael Deem.1

Historically, the influenza vaccine recommended by public health officials at the Centers for Disease Control and Prevention (CDC) during the 2016-2017 “flu season” only had an efficacy of 20 percent, and the pEpitope assessment predicted 19 percent efficacy for this vaccine.2 Full influenza vaccine efficacy data for the 2017-2018 flu season are still being compiled.

The majority of 2018-2019 influenza vaccines in the U.S. remain egg-based with two critical mutations in amino acids in one key region of the hemagglutinin protein, but the vaccine has an updated formulation to protect against H3N2.

“Our study found that these same mutations halved the efficacy of influenza vaccines in the past two seasons, and we expect they will lower the efficacy of the next vaccine in a similar manner,” Deem stated. He added that these adaptations are inevitable as long as most influenza vaccines are cultivated in eggs.

The Rice researchers believe the egg adaptations are the reason for the reduced efficacy. There are two new types of influenza vaccines available in the U.S. that do not use eggs for production, one uses MDCK dog kidney cells and the other uses army worm cells.3 When testing the efficacy of an experimental vaccine produced from insect cells, the Rice researchers predicted a higher 47 percent efficacy rate.1

However, according to a Kaiser Permanente study published Oct. 6, 2018, “Both cell-culture and egg-based inactivated influenza vaccine (IIV) vaccines showed relatively low vaccine effectiveness (VE) during the 2017-2018 influenza season in which the A(H3N2) virus strain dominated.”4

The full analysis of the Rice study was published in the September 2018 issue of the journal Clinical Infectious Diseases.2

References: