15. Prevnar 13

Prevnar 13
Some impending competition paints a dark image for Prevnar's future, unless Pfizer's own follow-up shot can hit the market running. (Pfizer)

15. Prevnar 13
2018 U.S. sales: $3.36 billion
Used for: vaccine for pneumococcal disease

Holding the reins as the top-selling vaccine in the world, Pfizer’s Prevnar posted another strong year of sales in 2018—even if growth was pretty flat. At $3.36 billion, U.S. sales grew roughly 1% year over year, helping to keep the shot at the top of Pfizer's sales charts.

But some impending competition paints a dark image for the future, unless Pfizer's own Prevnar follow-up can hit the market running.

Prevnar started off 2018 with troubling figures in the U.S. market as sales dipped 7% in the fourth quarter of 2017. The company had been warning that its new indications were tapping out: The “catch-up” population, created by a CDC recommendation in 2014, had essentially caught up.

And as Prevnar stagnated, Merck pushed forward its own candidate to take down the Pfizer shot. Dubbed V114, Merck's pneumococcal conjugate vaccine protects against 15 strains, including all 13 that Prevnar covers. Merck rolled out plans in April for two phase 3 studies pitting V114 directly against Prevnar.

Then, in June, another Prevnar challenger popped up. Biotech SutroVax garnered series C funding to develop its pneumococcal shot in a direct challenge to Pfizer.

Pfizer has its own plans for a next-generation vaccine, though. It's in the early stages of developing a pneumococcal shot that covers 20 serotypes. And to beef up vaccine sales further, it's entering later phases with its C. difficile and S. aureus shots.

15. Prevnar 13