In a statement released yesterday, Gottlieb cited less protection against the influenza A H3N2 virus as a chief reason for the low efficacy of the 2017-2018 flu vaccine. The Centers for Disease Control and Prevention (CDC) last month estimated this season’s flu vaccine to be 36% effective overall. Efficacy was estimated at 25% for influenza A H3N2, 67% for the influenza A H1N1 and 42% for influenza B.
“The current influenza season has been especially difficult, causing widespread illness that has affected all 50 states and resulted in a record number of hospitalizations. While healthcare professionals continue to combat this year’s flu — which may continue to affect Americans into April — we’re already partnering with other public health agencies to conduct essential work to produce next season’s influenza vaccines,” Gottlieb stated.
The CDC, when announcing its estimate in mid-February, reported that 69% of flu infections were caused by the influenza A H3N2 virus. That’s providing a springboard for the push to raise flu vaccine effectiveness, according to Gottlieb.
“As part of this process, we’re striving to better understand why we saw reduced effectiveness of this year’s influenza vaccines against one strain of influenza A, called H3N2. It was this strain that caused much of the influenza-related illness this flu season. Moreover, this year is not the first time we have seen vaccines be less effective against this particular strain of influenza, H3N2,” he explained.
“As such, we are taking a number of actions to better understand why effectiveness tends to be lower against the H3N2 strain and what we can do about it. By looking closely at the available data and applying the lessons we learn each flu season to the vaccine development process, we offer the greatest chance of developing vaccines that even more effectively prevent the flu in the future.”
As part of their effort, FDA scientists are collaborating with the Centers for Medicare & Medicaid Services (CMS) to use a large database containing details of the flu vaccines administered to 4 million people, as well as if they were hospitalized for flu or treated with antiviral medications for influenza-like illness.
Some areas of focus for assessing flu vaccine effectiveness, Gottlieb said, include the following:
• Egg-based development of flu vaccines versus cell-based or recombinant approaches. “The work conducted with CMS shows a preliminary finding that suggests the cell-based influenza vaccine might be somewhat more effective than the egg-based vaccine,” he stated.
• Comparing flu vaccine effectiveness in seniors administered the high-dose flu vaccine or the adjuvanted flu vaccine with those who received standard-dose flu vaccines. The adjuvanted influenza vaccine contains an ingredient to boost the immune system’s response to the vaccine, and the high-dose vaccines contain four times as much of the influenza antigen as standard vaccines.
• Age variations in effectiveness against influenza A H3N2. For children ages 6 months to 8 years, the vaccine’s efficacy against the A H3N2 virus was 51%, compared with 17% for seniors and even lower levels for older children and adults younger than 65.
• One theory is that people might require a higher amount of H3N2 antigen to elicit a proper immune response to that particular strain of influenza.
“There are a number of theories on why this season’s vaccines produced reduced effectiveness against H3N2. We’re taking steps to investigate each of these potential causes, rule out possible reasons for the variation in effectiveness and improve vaccine efficacy against H3N2,” according to Gottlieb.
“We would particularly like to understand why vaccine effectiveness against H3N2 influenza year to year tends to be lower than effectiveness against other influenza viruses,” he pointed.
Plans call for an FDA advisory committee to meet on March 1 to evaluate the recommendations of the World Health Organization (WHO) on the composition of flu vaccines for the Northern Hemisphere and help the FDA choose strains for next season’s vaccines. WHO has recommended changing two of the strains in this season’s flu vaccine for the Northern Hemisphere.
“The upcoming FDA advisory committee meeting will determine if these recommendations should also apply for the U.S. Following that meeting, the FDA will also work to apply all the knowledge that we gain from this year’s flu season to ensure that the best possible vaccines are available next season to protect against the flu,” Gottlieb added.