Food companies
Some food companies, like meat producer Tyson Foods Inc. (NYSE: TSN) and Smithfield Foods Inc. (NYSE: SFD), the largest pork (swine) product processor, saw substantial declines because of swine flu concerns. Already China has banned hog and pork product imports from Mexico and parts of the United States. Other countries have taken similar moves and some companies in the food sector may continue to suffer as long as this lasts. Hormel Foods (NYSE: HRL) is another such company.

Regions
Then there is Mexico itself. During SARS, many Asian stock markets, which was the hardest hit area, have seen large downswings. Similarly, Mexico, at the heart of this outbreak, may suffer. Perhaps even Latin America as a whole. UBS has downgraded the country's stocks to underweight.

Health care companies, drugstores
On the other hand, CVS Caremark Corp. (NYSE: CVS) and Walgreen Co. (NYSE: WAG) are trading higher as the two largest U.S. drug-store chains are preparing stores for a possible rush on hygiene products and pharmaceuticals. Similarly, makers of masks and other health care products could stand to gain.

Drug companies with stakes in flu vaccine making
Flu vaccine makers could make an even better bet. At least 20 companies make flu vaccines including Sanofi Pasteur, the vaccine division of Sanofi Aventis Group (NYSE: SNY), Australia's CSL Ltd, London-based GlaxoSmithKline Plc (NYSE: GSK), Novartis AG (NYSE: NVS), Baxter (NYSE: BAX), nasal spray maker MedImmune, acquired by AstraZeneca Plc. (NYSE: AZN) and Swiss based Roche (Other OTC: RHHBY) to name a few.

The main products that currently seem to work against this strain of flu are GSK's Relenza and Roche's Tamiflu, which was originally invented by Gilead Sciences Inc. (NASDAQ: GILD) and gets royalties from its sales. There are concerns, however, that Tamiflu -- taken orally in the form of a tablet -- might be less effective than Relenza, which is inhaled.

Currently, it takes months to make a flu vaccine and it could take years for drug makers to meet global demand. It's no surprise then that stocks of vaccine makers shot up globaly and in the U.S., especially those with licenses to make the aformentioend two drugs. GSK was the highest gainer. It's important to note that because of the avian flu, many governments already have substantial stockpile and the commercial effect could be muted.

Then there are the smaller companies like BioCryst Pharmaceuticals Inc. (NASDAQ: BCRX), which is working on an experimental flu vaccine and has surged over 85 percent. Similarly, Novavax Inc. (NASDAQ: NVAX) jumped nearly 125 percent, on its experimental vaccine to a deadly strain of bird flu.