The top 5 vaccine makers by 2013 revenue

Vaccines, which can be complicated and expensive to manufacture, haven't always been the moneymakers they are for some drugmakers today. Last year, the global vaccines market topped $25.56 billion according to EvaluatePharma, with the world's 6 top-selling shots each cracking the blockbuster barrier.

It's a small group of drugmakers that are enjoying vaccines' top-line success. The top three vaccine players--Merck ($MRK), Sanofi ($SNY) and GlaxoSmithKline ($GSK), in that order--generated nearly two-thirds of that haul, EP says. Add Pfizer ($PFE) and Novartis ($NVS) to round out the top 5, and the group raked in more than 86% of all vaccine sales.

And that club is only getting smaller. Back in April, No. 5 Novartis sold most of its vaccines unit to Glaxo as it made moves to exit the space. It's currently in the process of finding a buyer for its remaining lineup--a flu vaccines business that could help a rival pharma claw its way toward the top of the vaccines food chain or help a giant cement its leading position.

Of course, all of that could change as the cancer immunotherapy vaccine field takes shape. A host of contenders, from small biotechs to Big Pharma companies, is working to bring a new crop of therapeutic cancer fighters to a market that could one day be worth billions.

But for now, these 5 are at the front of the pack. Take a look at the report to see how they're doing it and what lies ahead as they look to maintain their leads--or bow out, as the case may be.

-- Carly Helfand (email | Twitter)