New York (CNN Business) Rite Aid is having quite a happy holiday. The company's stock has nearly tripled in 9 days after the drug store shocked investors with much-better-than-expected earnings.

The stock was up 15% Friday, soaring above $22 a share. On December 18, a day before the company announced its third-quarter earnings, Rite Aid was trading at just $8.32 a share.

Rite Aid RAD swung to a surprise profit in its last quarter, and Wall Street analysts severely underestimated the company's earnings. Rite Aid's adjusted profit was nearly eight times higher than analysts' expectations, boosted in particular by strong pharmacy sales . The company credited explosive growth in Medicare Part D membership as an increasingly large number of Baby Boomers sign up for government health care.

But front-of-store sales were better than expected too, growing 1% in the past quarter. Among the biggest contributors to the company's sales growth was Thrifty brand ice cream, which Rite Aid purchased in 1996. The company recently expanded the number of stores that sell Thrifty by 900.

The stock soared 42% on December 19, the same day it reported stellar earnings. But the stock has continued to rise every day since — 18.5% on the 20th, 7% on Monday, 7.5% on Tuesday, 19% Thursday and another 15% Friday.

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