Dividend stocks are a powerful way to boost the return on capital of any portfolio. That being said, it can be a chore to unearth income stocks worth owning for long periods of time. The fundamental problem is that most companies simply can't maintain their status as a top dog for lengthy periods of time. Moreover, the few publicly traded companies that can maintain a dominant competitive position -- especially those that pay attractive dividends -- tend to come with unsightly price tags. 

The blue-chip biotechs AbbVie (ABBV 0.92%) and Gilead Sciences (GILD -0.57%) are unique in this regard. Although both companies are smack dab in the middle of periods of transformation, they have been able to maintain -- and even grow -- their share of key disease markets. Nonetheless, the moody market has still seen fit to reward AbbVie and Gilead with clearance-rack valuations. AbbVie, for instance, is presently trading at a rock-bottom 9.19 times forward-looking earnings, and Gilead's stock is even cheaper at 9.09 times next year's projected earnings. Here's why income investors may want to scoop up some shares of these grossly undervalued dividend stocks soon.

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AbbVie: The hard part is over

AbbVie's stock hasn't gotten a whole lot of love from the market over the past year due to concerns over Humira's patent cliff. Humira is a popular anti-inflammatory medicine that also happens to be the best-selling drug in the world right now. However, the drug is widely expected to lose that title soon, thanks to the introduction of copycat medicines in key territories abroad. But this risk factor has arguably been blown out of proportion by investors over the prior 12 months. 

There are two reasons to believe this is the case. First up, AbbVie's immunology pipeline struck gold last year with the regulatory approvals for Skyrizi and Rinvoq. Both of these drugs are expected to quickly attain blockbuster status. Second, the biotech also inked a merger agreement with Allergan in 2019 -- a move that markedly lowers Humira's overall importance in terms of top-line growth and revenue generation. These recent developments essentially assure that AbbVie will continue to be a major cash cow for dividend and growth investors alike for years to come.

What does AbbVie offer on the dividend front? At current levels, AbbVie's stock is paying a forward-looking yield of 5.36%. That type of sky-high yield is extremely uncommon among large cap biopharmas. Now, the drugmaker's trailing payout ratio of 183% is on the high side. But AbbVie's proven ability to grow its top line at industry leading levels should comfort risk-averse income investors.

In all, AbbVie's bottom of the barrel valuation, junk-bond-like dividend yield, and strong track record as a top growth play make this stock an outstanding buy this year.  

Gilead: Safety, innovation, and financial firepower all in one package

Like AbbVie, Gilead hasn't exactly been a popular name among investors of late. Over the past three years, in fact, the biotech's shares have shed almost 40% of their value. Gilead's troubles stem from the fact that the company simply never found a viable replacement for its fading hepatitis C franchise as a source of top-line growth. Outside of HIV, Gilead's organic pipeline has woefully underperformed over the past five years. The good news is that an end to Gilead's trough period is within sight. 

Gilead's anti-inflammatory medicine, filgotinib, is widely expected to quickly reach blockbuster status, and the biotech's anti-cancer cell therapy franchise is also starting to gain ground with KTE-X19 likely to gain a key regulatory approval for mantle cell lymphoma later this year. Gilead also sports one of the highest cash positions in the industry, as well as exceptional free cash flows. Thus, the biotech has an immense amount of financial firepower for value-creating business development activities. 

How about the dividend? Gilead's shares sport an annualized yield of 4% right now. That is outstanding for a large-cap healthcare stock. Although Gilead does have a fairly high payout ratio of 116% at current levels, this issue shouldn't overly concern income investors. The biotech's top line should pick up in a big way soon. In other words, Gilead won't have any problem covering -- and perhaps growing -- its dividend.  

All told, Gilead's days as an out-of-favor biotech stock seem close to an end. Income investors, in kind, may want to get in ahead of the crowd to take advantage of the biotech's rather generous yield and improving outlook.