As winter approaches in the Northern Hemisphere, flu is likely to follow quickly after.
Concerns that the virus could mean an increase in staff sick days has prompted some companies to arrange flu jabs for their employees – boosting sales for some drugs companies.
"The fear factor has led to a lot of people who wouldn't have considered taking it doing it. From a corporate point of view, if you can prevent people being off, that would be helpful," Naresh Chouhan, pharmaceuticals analyst at Liberium, told CNBC.
GSK, Merck, AstraZeneca and Sanofi stand to benefit most from increased vaccine take-up by governments and businesses, Chouhan said. Rival Novartis has slipped behind slightly because of production problems.
Sanofi Pasteur, the Sanofi unit and the world's biggest supplier of flu vaccines, generated flu jab sales of 884 million euros ($1.43 billion) in 2012.
If fewer people suffer from prolonged bouts of flu as a result of vaccination, the companies who produce treatments for it, like Reckitt Benckiser who had a weak flu season in the winter of 2011/12 according to Deutsche Bank analysis, will have less lucrative sales.
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Several pharmaceutical companies made a conscious decision to chase and develop the vaccines market towards the end of the last decade, as it became clear that the traditional blockbuster drug treatment model for the industry was changing. Vaccines were seen as promising from a business perspective because they could be applied to huge swathes of the population, and because the economic case for payment could be made to governments. AstraZeneca, the U.K. pharmaceuticals giant, paid $15.6 billion for MedImmune, the U.S vaccines specialist, in 2007 to get a foothold in the vaccines market.
Chris Viehbacher, chief executive of Sanofi, explained part of the appeal of vaccines earlier this year. "The nature of vaccines is such that generally you have a better feeling for the success of a vaccine than you do for a new drug," he said.
"Even at an average price level you get to some pretty significant sales."
There have been significant scientific advances in the area, which have made it easier to justify charging a price premium – and harder for generic rivals to launch cheaper copycat treatments.
And there is still a significant population which does not get a regular vaccine to be targeted. Around two-thirds of U.S. adults didn't get a flu shot last year, according to a talk by Erin D. Kennedy at the National Adult and Influenza Immunization Summit earlier this year.
"Vaccination is considered the most effective way to prevent infection from flu," according to a spokesman for GSK.
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This year is the third flu season since the U.S. began to recommend a seasonal flu vaccine, following the outbreak of the "swine flu" or H1N1 pandemic. It is also the first flu season when vaccines to treat four different strains of flu, two of influenza A and two of influenza B, will be available.
They will come at a cost to governments and businesses. GSK's new version of its Fluarix vaccine, which treats four instead of three strains of flu, will cost the U.S. government $12.03 per dose, compared to $8.08 per dose for the older version (see here for more on U.S. vaccines pricing).
"You can charge much more in the U.S. for a flu jab, so the U.S. will always be prioritized," Chouhan said.
- By CNBC's Catherine Boyle. Twitter: @cboylecnbc.