The mosquito-borne virus endangers one of the most vulnerable groups of society, pregnant women. 

But many athletes and spectators -- men and women -- have been alarmed enough not to attend the summer Olympics in Rio de Janeiro over concerns about Zika in Rio de Janeiro.

Zika, which can lead to paralysis and birth defects, highlights the demand for cures and vaccines. Such products are where pharmaceutical and biotech firms can make big money, and can benefit investors. Savvy investors should be watching firms that are in the forefront not just of Zika research but also in the development of other vaccines. We've identified three firms to watch below.

To be sure, there are other companies that have promising products and bear watching.

VBI Vaccines (VBIV - Get Report)  is starting an FDA phase 1 trial for the cytomegalovirus. This virus can cause death and birth defects such as microcephaly in babies, just like Zika. However, it's a lot more common and can spread in areas where the Zika-carrying mosquito can't go.

VBI's vaccine uses a technology called an enveloped virus-like particle (VLP) that mimicks how viruses travel through the body's systems. This makes the vaccine all the more effective. VBI has already successfully tested a VLP vaccine for hepatitis B.

But the ranks of pharma and biotech firms include many companies that failed because they couldn't bring once-promising products to market. VBI is more of a play for an aggressive investor who is willing to gamble that the company will win FDA approval. But if you're a risk averse investor, the larger players with multiple products already on sale are better plays. 

They are worthy of your investing dollars.

1. Pfizer (PFE - Get Report)

With a market cap over $217 billion, Pfizer is a giant. But the company is poised for even more growth thanks to its growing vaccine portfolio. Leading the pack is Prevnar, a vaccine to prevent pneumonia. For the most recent quarter, Prevnar revenues were up more than 16% year over year. Pfizer is currently working on developing a vaccine for Zika. The company helped its cause last year by acquiring Redvax. Many of Redvax's vaccines use virus-like particle technology similar to VBI's. Investors should get in now.

2. Merck (MRK - Get Report)

Merck recently announced a partnership with Modena Therapeutics to develop and market cancer vaccines. The company is the maker of Gardasil, an extremely popular human papillomavirus (HPV) that uses VLP technology. HPV causes genital warts and has been linked to a number of different cancers. Researchers recommend that adolescent and teenage girls receive a vaccination to prevent the disease. 

HPV Merck currently makes the world's leading hepatitis B vaccine, Recombivax.

Merck is currently trading around $58, near its 52-week high of $60.07. But the revenues from the vaccines business could push the stock higher. As the public clamors for preventative therapies, investors should see steady profits.

3. GlaxoSmithKline (GSK - Get Report)

GlaxoSmithKline and Pfizer have made more than $30 billion in the last seven years from pneumonia vaccines alone. The company also stands to benefit from the eVLP technology of VBI. GlaxoSmithKline and VBI are partnering to develop and market the hepatitis B vaccine. The mega drugmaker is also currently analyzing data to determine if it can harness its current dengue fever vaccine to create a preventative treatment for Zika.

GlaxoSmithKline is an unbeatable moneymaker that hauls in money yearly. 

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This article is commentary by an independent contributor. At the time of publication, the author held no positions in the stocks mentioned.