Huh? The FDA's main guidance document on this topic, issued in 2007 with no major overhaul since [0], states that comparative efficacy or effectiveness data is valuable when:

- The comparator vaccine is indicated for the same population.

- The comparator has existing clinical effectiveness data.

In other words, the trial design should use a benchmark that makes sense given what doctors and guidelines actually recommend today. For older adults, evidence over the past 15+ years has shown that enhanced flu vaccines often provide better protection than standard-dose ones. The study used standard-dose vaccines as far as we can see.

The only oddity here is that the FDA apparently approved the study previously

[0] https://www.fda.gov/regulatory-information/search-fda-guidan...