If you thought the fireworks ended after the Fourth of July celebrations last week, think again. Plenty of pops and bangs were heard in the world of health-care stocks this week. Here are three of the biggest and brightest.

Successful launch
You couldn't even buy stock in Prosensa (NASDAQ: RNA) just a few weeks ago. The biotech launched its IPO on June 28. To say that launch has gone successfully is an understatement. Shares are now more than double the IPO price and climbed 41% this week.

This rapid rise stems from investor excitement that Prosensa's drisapersen received breakthrough therapy designation from the Food and Drug Administration. The FDA's move could allow Prosensa and its partner GlaxoSmithKline (GSK -0.92%) to beat Sarepta Therapeutics (SRPT 6.09%) in the race to bring a Duchenne muscular dystrophy drug to market first.

So far, Prosensa's gains haven't been at Sarepta's expense -- just as I suspected would be the case. For Sarepta, winning accelerated approval for eteplirsen is the most important factor, regardless of what happens with drisapersen. For Prosensa, gaining an early-bird advantage could make some of the other drugs in its pipeline attractive to Glaxo, which has options on several drugs in the small biotech's portfolio.

Early validation
Alnylam Pharmaceuticals (ALNY -1.55%) was another big winner this week, with shares jumping 32%. Good news from an early-stage study powered the stock's climb.

The biotech reported on Thursday that its experimental drug ALN-TTRsc reduced levels of the TTR protein by 80% in a trial involving healthy individuals. High levels of this protein can result in degenerative disease. The effectiveness of ALN-TTRsc in knocking down TTR raises the chances of success for Alnylam's platform of RNAi therapeutics beyond this one drug.

Alnylam will present data from the study at the September meeting of the Heart Failure Society of America. The biotech plans to begin a phase 2 study for ALN-TTRsc targeting treatment of familial amyloidotic cardiomyopathy, a rare degenerative disorder that affects around 40,000 patients worldwide. If all goes well, a phase 3 study will follow in 2014.

Turnaround turns heads
WebMD (WBMD) attracted plenty of investor attention on Friday, with a sneak peek at its second-quarter results. Shares soared 26% on the surprisingly good news from the online health information provider.

Reduced spending on drug ads contributed to woes for WebMD last year. In December, the company cut around 14% of its staff in an effort to control spending in the face of lower revenue. This belt-tightening combined with a rebound in ad spending by customers helped WebMD beat expectations on both the top and bottom lines.

The turnaround has WebMD optimistic about the remainder of the year. The company now projects revenue of $485 million to $505 million and earnings between $3 million and $11 million. That's a solid upward revision from the $450 million to $470 million in revenue and loss of $1.5 million to $13 million WebMD provided as guidance earlier.

Picks of the week
Are any of these humongous stocks of the week likely to see more fireworks in the future? I'd say that could be the case for Alnylam. The good news this week was just for one drug in a phase 1 trial. There's plenty of risk, of course, but this biotech could see more pops down the road.

If Prosensa and Glaxo beat Sarepta in commercializing the first drug for DMD, Prosensa should also see shares go even higher than they already have. I expect the stock to be quite volatile as the race continues, however.

The most solid pick of the bunch is WebMD. It has a trusted brand and great product offerings. I had questions in the past if the management team could right the WebMD ship. These questions now appear to be answered positively.