Some investors got to open their presents early this week. These three health-care stocks delivered big-time over the past few days. Here's what happened.

Hip, hip, hooray
Coming in at the top of our list is Enanta Pharmaceuticals (ENTA -1.75%). Shares of the drug developer shot up 34% this week after great news was announced by its partner AbbVie (ABBV -1.03%).

On Tuesday, AbbVie reported results from a phase 3 study of a direct-acting antiviral combo used in treating patients with chronic, genotype 1 hepatitis C virus, or HCV, infection. Those results were simply outstanding, with 96% of patients who had previously failed pegylated interferon and ribavirin treatment achieving sustained virologic response at 12 weeks. That's very good for AbbVie, which is in a tight race in the hep-C market.

It's also fantastic news for Enanta. One of the three drugs in AbbVie's combo was Enanta's ABT-450. AbbVie also has several other clinical studies under way with ABT-450 as well as well as early stage studies involving another Enanta HCV drug, ABT-493. 

Picture perfect
Shareholders of "camera pill" maker Given Imaging (NASDAQ: GIVN) enjoyed a picture-perfect week. Given's shares soared over 26% after big health-care products company Covidien (COV.DL) announced an acquisition of the smaller gastrointestinal diagnostics systems maker.

Under the terms of the deal, Covidien will pay $30 per share -- around $860 million in total net of cash and investments acquired with the buyout. In return, Covidien gains an opportunity to expand its presence in the multibillion-dollar gastrointestinal market.

Given's PillCam proved a tempting target. The technology first introduced more than 12 years ago allows clinical professionals to view a patient's digestive system after the patient swallows a pill containing a tiny camera. Covidien's proposed acquisition now requires approval by Given Imaging shareholders. Assuming approval on that front and no problems with regulators, the deal should close by the end of the first quarter of 2014.

Five out of eight ain't bad
You have probably heard the old expression "two out of three ain't bad." This week, Corcept Therapeutics (CORT -2.26%) found that five out of eight ain't bad, either. Positive results from five patients in an eight-patient clinical study sent Corcept's shares upward by 23% for the week.

In the phase 1 study led by the University of Chicago, five patients with relapsed metastatic triple-negative breast cancer, or TNBC, achieved a partial or complete clinical response to treatment with mifepristone plus chemotherapy. Mifepristone is Corcept's glucocorticoid receptor antagonist that is already on the market as a treatment for controlling hyperglycemia associated with Cushing's syndrome, a rare endocrine disorder.

As a result of the positive study results, Corcept now plans to expand its development program into oncology. The company filed an investigational new drug, or IND, application with the U.S. Food and Drug Administration to study the effects of mifepristone in treating TNBC.

Best gift
Which of this week's humongous health-care winners could be the best gift to investors in the days ahead? I'll go with Enanta.

The upside for Given's shareholders is, well, a given -- since we know how much Covidien is paying to scoop up the company. Corcept's news is great, but we're still only looking at early stage results with a small number of patients.

Enanta, on the other hand, benefited from results from a large late-stage study. If AbbVie ultimately gains regulatory approval for its HCV regimen, Enanta's shares will undoubtedly vault significantly higher, even after this week's huge gains. This pharmaceutical company's stock could be the gift that keeps on giving.