The top 5 vaccine makers by 2013 revenue

1. Merck
2013 sales: $5.77 billion

It's not hard to see how Merck's ($MRK) leading the worldwide vaccines market. The New Jersey pharma giant had 5 of the 10 best-selling vaccines in 2013, including Gardasil in the No. 2 spot. Merck's sales of the HPV jab swelled 12% last year to reach $1.8 billion; the vaccine, marketed in Europe by Merck's JV with Sanofi Pasteur, generated $2.17 billion overall.

And Gardasil has gotten some recent boosts that could lift sales further in the not-too-distant future. It recently scored an EU nod for preventing anal cancer, and back in April, the European Commission approved a two-dose regimen that the company said it thinks could expand coverage and increase uptake.

In February, the FDA also accepted Merck's application for V503, a Gardasil follow-up that analysts estimate could pull in $1.9 billion in peak sales. But most of those will come at Gardasil's expense: Leerink Partners estimates peg Gardasil's 2018 sales at just $525 million.

Backing up Gardasil on the current top-sellers list are fellow blockbuster Varivax, ranking 5th with $1.38 billion in 2013 sales; herpes shot Zostavax, which brought in $826 million to earn the 8th spot; rotavirus vaccine RotaTeq, hauling in $691 million to secure 9th place; and Pneumovax, rounding out the top 10 with $653 million.

For more:
Merck JV plans to show up J&J, Sanofi with low-cost cholera vaccine
Merck, Sanofi JV wins anal cancer indication for Gardasil in EU
Merck's RotaTeq, Glaxo's Rotarix cut hospitalizations by up to 94%
Study: Moral concerns lead barriers to Gardasil uptake in college freshmen