GlaxoSmithKline

3. GlaxoSmithKline
2013 sales: $5.35 billion

Glaxo's ($GSK) vaccines haul may have declined by 2% last year, thanks to an adverse comparison with strong Japanese sales of Cervarix as part of the country's HPV catch-up program. But after an April agreement to buy most of Novartis' ($NVS) vaccines unit, it's about to get a substantial boost.

The $7.1 billion deal, expected to close next year, will send Novartis' lineup and pipeline--excluding flu products, which GSK already has--to the British drugmaker. One highlight among them: Bexsero, the world's first marketed shot to protect against deadly meningitis B, recently launched in Europe and awaiting regulatory approval in the U.S.

In the meantime, Glaxo will rely on blockbuster shot Pediarix, which pulled in $1.35 billion in sales last year, and its hepatitis franchise, which generated $984 million. Its new quadrivalent vaccines for seasonal influenza are gearing up for their sophomore campaigns, too, after driving a 76% sales jump in last year's fourth quarter.

But Glaxo's flu vaccines aren't necessarily all ready to roll: The company is taking heat from two regulators over problems at its Ste-Foy, Quebec, plant, the home of manufacturing for FluLaval. Both the FDA and Health Canada are pressing Glaxo to address bacteria-related problems and other issues at the facility, which is slated to provide about 23 million of the 28 million to 33 million doses of flu vaccine that Glaxo will supply the U.S. with this year.

For more:
Out with the new and in with the old after GSK trips up at vaccine plant
Novartis' soon-to-be-Glaxo's vaccine unit sees mounting losses, diving sales in Q2
As Glaxo begins 2014-15 flu vaccine shipments, manufacturing questions linger
Canada gives GSK 30-day deadline for turnaround plans at FluLaval plant
Novartis bids farewell to vaccines with $7.1B sale to GSK