Amid an industrywide look into pharma's pricing, Sanofi has pledged to limit its drug price hikes to the rate of medical inflation. The company recently tweaked its policy to provide rationale for any hikes above that level, and in the first year of the policy, detailed a 12.5% increase for a flu shot picked up through M&A.

Last year, the company's only product to get a price hike above the U.S. National Health Expenditure growth rate was recombinant protein-based flu vaccine Flublok, acquired in the $650 million Protein Sciences buyout. Another 28 price hikes at the drugmaker fell within the NHE growth rate. Early every year, the Centers for Medicare and Medicaid Services establishes the rate; last year, it was 5.4%.

The rationale for Flublok's hike? Sanofi pointed to a study published in the New England Journal of Medicine last June showing that Flublok was 30% more effective than GlaxoSmithKline's Fluarix Quadrivalent at preventing lab-confirmed flu illnesses in people 50 and older.

Sanofi increased the vaccine's price 12.5%—to $45 per dose from $40 per dose—based "on an assessment of recent clinical efficacy data demonstrating that the Flublok vaccine delivers substantial benefit" over a standard flu shot, according to a pricing document (PDF) published last month.

Sanofi's vaccine sales were €1.59 billion ($1.86 billion) last year, up 8.2% versus the prior year.

Meanwhile, Sanofi and other drugmakers are advancing technology to improve on traditional flu vaccine technology, which has faced scrutiny recently for efficacy problems. Last year, the egg-based production method was faulted for a lower-than-desired efficacy against the H3N2 flu strain, which tends to cause more severe illness. Overall, flu vaccines were 36% effective for the flu season, but officials noted that non-egg-based options seemed to provide better protection, triggering more interest in alternative options.

Flublok Quadrivalent is made using insect cells and won approval in 2016 as the only recombinant protein-based flu shot to protect against four strains. Seqirus also markets cell-based flu shots under the name Flucelvax.