The top 5 vaccine makers by 2014 revenue

2014 sales: $6.25 billion

Merck ($MRK) came out as the top vaccine maker last year, and it's done so again. The company reeled in $6.25 billion in 2014, an 8% increase over the $5.77 billion it generated in 2013. This was largely thanks to Gardasil, which remains the second top-selling vaccine worldwide. 2014 sales of the HPV jab jumped to $2.03 billion, $2 million more than its 2013 number, an increase of almost 11%.

Its follow-up, Gardasil 9, which protects against 5 further strains in addition to the four originally targeted by Gardasil, won FDA approval in December and an EMA nod in June to market it in Europe. While low uptake of Gardasil had analysts revising their sales predictions for the jab--estimates that went as high as $10 billion annually--Gardasil 9 has the potential to block 90% of cervical cancers and rake in the sales associated with widespread vaccination. But to do so, the company has to address factors that has slowed its predecessor's uptake: sex-related stigma, reimbursement problems for boys and a three-shot regimen.

And competition for Gardasil is slowly creeping up. A study published in June showed that one shot of GlaxoSmithKline's ($GSK) Cervarix might offer the same protection as multi-dose regimens of Cervarix and Gardasil, and India's Serum Institute is working on a vaccine that could be ready by late 2018 at one-third the price of Gardasil.

Other top-earning vaccines include M-M-R, Varivax and ProQuad, which protect against measles, mumps, rubella and varicella. The trio brought in $1.39 billion in 2014. Merck also markets Zostavax, the only shingles vaccine approved for human use. While M-M-R sales skyrocketed in early 2015 in response to a measles outbreak in Disneyland, Big Pharma peer GSK is working on its own rival to Zostavax, which, in Phase III, showed higher efficacy, and, significantly, higher efficacy in older adults. This had analysts predicting that after approval, GSK's candidate would be "well-positioned" to snag market share from Zostavax.

Also in the works is an Ebola vaccine, on which Merck is collaborating with NewLink ($NLNK). According to interim results, the candidate posted 100% efficacy in a large Phase III trial in West Africa.

-- Amirah Al Idrus

For more:
Merck's Ebola vaccine is 100% successful in interim Phase III results
European safety watchdog digs into HPV vaccines again
One dose of GlaxoSmithKline's Cervarix may suffice
Whistleblowers accuse Merck of withholding info on mumps vaccine
As California measles cases mounted, so did Merck measles vaccine sales
Merck injects another $12.4M in its newest vaccine plant