We might be in the so-called dog days of summer, but that doesn't necessarily apply to stocks. At least not all of them.

Three stocks, in particular, soared at least 20% this week. Health Insurance Innovations (NASDAQ:HIIQ), DexCom (NASDAQ:DXCM), and Molina Healthcare (NYSE:MOH) enjoyed huge runs over the last few days. What lit a fire beneath these stocks -- and are any of them still smart picks for investors to buy now?

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1. Health Insurance Innovations: Trumping expectations

Shares of Health Insurance Innovations skyrocketed nearly 43% this week due to two positive news stories. One related to the cloud-based health insurance platform company's better-than-expected Q2 earnings results. The other came from the Trump administration's new rule that could shake up the individual health insurance market.

Let's start with Health Insurance Innovations' Q2 results. The company reported record revenue of $71.7 million, up 16% from the prior-year period. Adjusted earnings per share jumped 32.6% year over year to $0.61, handily beating analysts' estimates. The company also boosted its full-year 2018 revenue and adjusted earnings guidance.  

As good as Health Insurance Innovations' second-quarter news was, the latest regulatory update from the White House should be even better for the company over the long run. Beginning Oct. 1, short-term health insurance plans with durations less than 12 months will be allowed in the U.S. In the past, the duration of short-term plans was limited to less than three months. In addition, insurers will be able to renew these short-term plans for up to 36 months.

Because these short-term plans don't have to meet all of the criteria imposed by the Affordable Care Act (popularly called Obamacare), their costs should be significantly lower than other individual health insurance. This should present a great market opportunity for Health Insurance Innovations.

2. DexCom: Monitoring progress

DexCom stock jumped 29% this week after the medical-device maker reported strong second-quarter results on Wednesday. As you might expect, those results looked pretty good.

The company's revenue increased 42% year over year to $242.5 million in Q2. This reflected 35% growth in the U.S. and 78% growth in international markets over the prior-year period. DexCom CEO Kevin Sayer attributed this success to increased adoption of the company's continuous glucose monitoring (CGM) products.

What's especially encouraging is that DexCom's newest CGM system -- its G6 product -- didn't launch until late in the second quarter. That bodes well for the company's fortunes in the rest of 2018 and into next year. It was no surprise that DexCom raised its full-year 2018 revenue guidance to $925 million from its previous outlook of between $850 million and $860 million. DexCom isn't profitable yet, however.

One of the biggest opportunities for DexCom is integrating its CGM systems with automated insulin pumps in what's called a closed-loop solution. Tandem Diabetes Care plans to launch its new automated insulin pump that integrates with DexCom's G6 CGM this month.

3. Molina Healthcare: Make it a double

Shares of Molina Healthcare rose nearly 21% this week. The reason behind the managed care company's nice gain is a familiar one: Molina announced its Q2 earnings results on Tuesday.

The company's revenue declined 2.3% year over year to $4.88 billion. So why did the stock perform so well? Molina's bottom line improved dramatically. The company went from a loss of $4.10 per share in the prior-year period to positive earnings of $3.02 per share in the second quarter. Wall Street expected earnings per share of $1.08. I'd call that a pleasant surprise.

Even better, Molina revised its full-year 2018 earnings guidance -- by a lot. The midpoint of the company's previous guidance in February projected 2018 earnings of $219 million at the midpoint. Molina now expects earnings this year will be between $471 million and $484 million. The low end of that range is still more than double Molina's previous guidance. 

Are they buys now?

In many cases, big spikes like Health Insurance Innovations, DexCom, and Molina enjoyed this week quickly fade away. Investors hoping to ride the momentum end up being disappointed. I don't think chasing momentum is a smart strategy, but I actually like all three of these stocks over the long term.

Americans with incomes low enough to receive federal subsidies have been helped by Obamacare. However, for many in the middle class, the higher premiums resulting from Obamacare have been hard to handle. I think Health Insurance Innovations will benefit tremendously from the individual health insurance market changes that are being implemented.

DexCom's G6 CGM is providing the boost that the company needed. Diabetes currently ranks as the No. 7 leading cause of death in the U.S. It's also the fastest-growing chronic disease in the world. I think the diabetes market will continue to be large enough to support multiple winners -- and I think DexCom will be one of those winners.

As for Molina, my view is that managed care is here to stay and that it will become even more critical for Medicaid programs. Despite its big run in 2018, Molina's earnings growth prospects still make the stock's valuation attractive. I wouldn't be surprised if the company is acquired by a larger player within the next few years. 

Are there even better stocks to buy right now? Yes. However, my prediction is that Health Insurance Innovations, DexCom, and Molina will generate solid returns for investors over the next several years.

Keith Speights has no position in any of the stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. The Motley Fool has a disclosure policy.