I know I'm in trouble when I first hear about an infectious disease problem through the lay press. In the case of this year's flu vaccine, it was NPR, about a week ago. It looks like it started turning up on some national news feeds a few days earlier, and the message was that estimates of vaccine efficacy from Australia (the southern hemisphere flu season is winding down) were around 10%.
As is my usual practice, I go to the source data, which in this instance wasn't easy since virtually none of the lay press announcements included a link to that source. I finally traced it back to an online publication from October 26, 2017, and I'm still wondering why it didn't make more a splash back then, rather than 6 weeks later.
Based on interim reports of flu activity in Australia through late September, investigators did determine vaccine efficacy to be 10% (95% confidence interval -16 to 31) for influenza A H3 strains for all age groups; A H3 are the most common strains circulating this season. They used a test-negative study design for flu-positive patients seeking medical attention in sentinel clinics, which is a standard approach for flu vaccine efficacy research. Overall vaccine efficacy against all subtypes of influenza A and B was a more respectable 33% (17 to 46). Efficacy against A H3 strains varied by age. Children under 15 years of age and adults 15-64 years experienced rates of about 15% efficacy, while adults 65 and older having essentially no efficacy for A H3 strains. These numbers, if true, are not unprecedented with A H3 strains and have resulted in heavier flu seasons in the past.
It's too early to tell whether these estimates will hold for Australia once all data are available, and of course it's still too early to make an estimate for the US. A season with lower vaccine efficacy can mean greater risk of serious outcomes in high-risk populations, and this risk will be even greater if news about the lower efficacy results in fewer people seeking immunization this year. For now, it's important to stress that everyone should be immunized for influenza.
You can keep track of influenza season at the CDC and the Maryland Department of Health websites.
What flu vaccines are cell based? The October article stated that the US makes cell based flu vaccine which should be more effective than egg based for H3. Are cell based vaccines available for children? And if they are, should we be vaccinating high risk kids with it?
A great question, Ashley. Probably a better verb to use in your 2nd sentence is "might be" rather than "should be." Most flu vaccines are made in chicken eggs, and 1 problem that occasionally occurs is that the flu strains "adapt" to growth in this setting that might change how the vaccine elicits antibody to the haemagglutinin portion of the virus (the H in H3). Cell-based vaccines are grown in tissue culture and seem to have less of this egg-adaptability problem. So, in theory, cell-based vaccines might work better, but we don't know this for sure. At this time, authorities are not recommending preferentially using cell-based vaccines over other flu vaccines for any particular population, including high-risk individuals.
In the US, 1 cell-based vaccine is licensed for use in children at 4 years of age and up. You can look up the package insert details on the FDA website at https://www.fda.gov/BiologicsBloodVaccines/Vaccines/ApprovedProducts/ucm502844.htm.
Bud