Americans may just now be gearing up for flu season, but scientists in laboratories across the world have been prepping for it all year, aiming to answer that perennial question: What flu shot recipe will best prepare people for the flu viruses coming around next?

But despite all their research, flu shots have only a coin-toss's chance of working on whatever the year's dominant B-lineage flu strain (one common type of flu, along with influenza A) turns out to be. While doctors and health professionals encourage everyone over 6 months of age to get an annual flu shot, they acknowledge that the vaccine can be hit-or-miss. "This is a virus that's a constant moving target," says Carolyn Bridges, a doctor and the associate director for adult immunizations at the Centers for Disease Control. The flu is more dynamic than many other diseases, morphing so often that researchers have to formulate a new vaccine almost every year, Bridges says. Even so, matching the vaccine to the flu strain that ends up dominating that season is a puzzle, and doesn't always work; in the 1997-98 season, the flu shot had "no benefit whatsoever," Bridges says. Complicating the problem further, for the past decade, two very different B-strains of the flu have circulated, but vaccines have only targeted one. Indeed, in the 12 flu seasons since 2000, the vaccine has only matched the dominant B-strain half of the time.

Now, pharmaceutical companies are finally coming up with new vaccine formulations designed to better prevent whichever type of flu ends up going around. The new products, known as quadrivalent influenza vaccines, contain four flu strains instead of three and are expected to become available to consumers starting in the 2013-14 flu season. That could be good news for patients and investors alike: A CDC analysis of 10 flu seasons found that a four-strain vaccine could have prevented nearly 3 million flu cases and 1,400 flu-related deaths.

Of course, health experts say that while people who get the new vaccines will be better protected from more types of flu, there is still no guarantee they won't get sick. But investors don't have to wait to inject their portfolios with potential benefits of the new flu vaccines. While Morningstar analyst Damien Conover says the new products won't necessarily unlock new market opportunities compared with the older vaccines, they will likely generate sales for a few publicly traded companies.

The first quadrivalent vaccine to be approved by the FDA is a new nasal spray product called FluMist Quadrivalent, from AstraZeneca's (AZN) biologics arm MedImmune (the company plans to start distributing it for the 2013-14 flu season). A spokesperson for MedImmune says its forthcoming product is designed "to help provide broad protection" against two types of circulating influenza.

GlaxoSmithKline (GSK) is also developing quadrivalent versions of its flu shot, Fluarix, which it says will improve seasonal flu vaccines. The company expects to license one product in December and the second next year, according to an October presentation for the CDC. The company declined to comment because of the vaccine's investigational status, but said in a statement in October that the addition of a fourth strain to the product is designed to "potentially help broaden protection" against the flu and that studies have shown the vaccines to be "highly immunogenic" against all four strains.

The vaccines division of Sanofi (SNY), Sanofi Pasteur, plans to begin distributing its quadrivalent flu vaccine in the fall of 2013, pending FDA approval and availability of the product, according to the company's CDC presentation. A Sanofi Pasteur spokesperson says that it can't guarantee that its new offering will match all flu strains circulating that year because "the problem with creating an influenza vaccine is that the flu is unpredictable, and its strains change over time." But adding the fourth strain could have a "substantial impact" in reducing cases of flu and related complications and deaths. This could translate into benefits to public health and ultimately investors, the spokesperson says.