Merck (NYSE:MRK) turned in a really good performance the last time it reported its quarterly results in April. The big drugmaker handily topped Wall Street analysts' revenue and earnings estimates, with cancer immunotherapy fueling much of its growth.

If there were any doubts as to whether Merck's momentum would continue in the second quarter, they just disappeared. Merck announced its Q2 earnings results before the market opened on Tuesday. And the company yet again hit the bull's-eye. Here are four key things you need to know about Merck's fantastic Q2 results.

Arrow with dollar sign hanging from end stuck in bull's-eye on target

Image source: Getty Images.

1. Merck trounced analysts' estimates

Wall Street analysts might need to dial up their optimism a bit when projecting how Merck will perform. Merck again trounced analysts' estimates on both the top and bottom lines in the second quarter.

The company reported Q2 revenue of $11.8 billion. This reflected a 12% year-over-year jump and a 15% increase on a constant currency basis. The consensus analyst estimate called for Q2 revenue of $10.96 billion.

Merck also announced earnings of $2.7 billion, or $1.03 per share, under generally accepted accounting principles (GAAP). The company's GAAP earnings per share (EPS) in Q2 were 63% higher than in the prior-year period.

The drugmaker posted non-GAAP (adjusted) EPS of $1.30, up 23% year over year. This easily beat the average analyst estimate of $1.16.

2. Keytruda sales skyrocketed

Those impressive revenue and earnings beats were made possible largely by Keytruda. Sales for the powerhouse cancer drug skyrocketed 58% year over year to $2.6 billion. Adjusting for currency fluctuations, Keytruda's sales were 63% higher than in the prior-year period.

The primary factor fueling Keytruda's sales growth was its continued strong momentum in the non-small-cell lung cancer (NSCLC) indication. However, the recent launches of the drug in treating renal cell carcinoma (RCC) and adjuvant melanoma also contributed to Keytruda's ongoing success.

Market researcher EvaluatePharma projects that Keytruda will be the top-selling drug in the world by 2024 with annual sales of $17 billion. That prediction seems increasingly more likely to become reality with the continued strength that Keytruda is exhibiting.

3. Vaccine sales soared, too

Keytruda wasn't the only big hit in Q2. Merck's vaccine franchises also performed exceptionally well, with the overall human health category jumping 33% year over year to $2 billion. Excluding the impact of foreign exchange, vaccine sales soared by 36%.

Human papillomavirus (HPV) vaccine Gardasil looked especially strong, with sales zooming 46% higher than the prior-year period to $886 million. Merck attributed this tremendous growth primarily to public sector buying patterns, stronger demand and higher prices in the U.S., and its ongoing launch of Gardasil in China.

The company's pediatric vaccines also generated solid growth. Sales for measles, mumps, and rubella virus vaccine M-M-R II; chickenpox vaccine Varivax; and measles, mumps, rubella, and varicella virus combo vaccine ProQuad together increased by 58% year over year to $675 million. 

4. A great year is looking even greater

Three months ago, Merck expected full-year 2019 revenue of between $43.9 billion and $45.1 billion, with adjusted EPS between $4.02 and $4.14. After the company's stellar second quarter, Merck raised and narrowed its guidance for both revenue and adjusted EPS.

The drugmaker now projects full-year 2019 revenue will be between $45.2 billion and $46.2 billion. Merck also expects adjusted EPS for the full year will land between $4.84 and $4.94.

Again, it seems that Wall Street analysts will have to boost their outlook. Prior to Merck's Q2 results, analysts were projecting full-year 2019 revenue of $44.74 billion and adjusted EPS of $4.75.