Moderna or Merck: Which Soaring Cancer Vaccine Stock Is the Better Buy?

The companies said the improvements versus Keytruda alone were both statistically significant and clinically meaningful. Importantly, this represents the first positive Phase 3 readout for an individualized neoantigen therapy and an mRNA-based cancer therapy.

Investors have responded accordingly. Moderna shares have more than doubled intraday, while Merck stock has jumped over 10%. The question is whether investors should chase either stock after today's enormous move.

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Why the Cancer Vaccine Data is Such a Big Deal

Moderna’s intismeran is individually manufactured using mutations identified from each patient's tumor and can encode up to 34 neoantigens intended to teach the immune system to recognize cancer cells. It is then paired with Merck’s Keytruda, which helps remove mechanisms cancer cells use to evade an immune response.

The Phase 3 success also validates encouraging earlier results. Five-year Phase 2b data showed that intismeran plus Keytruda reduced the risk of recurrence or death by 49% and the risk of distant metastasis or death by 59% compared with Keytruda alone.

That said, the companies have not yet disclosed the detailed Phase 3 efficacy numbers, making the eventual medical-conference presentation an important catalyst. They intend to discuss potential regulatory submissions with authorities. Meanwhile, the broader INTerpath program includes nine Phase 2 and Phase 3 trials across cancers including melanoma, non-small cell lung cancer, bladder cancer, and renal cell carcinoma.

That pipeline breadth is particularly important for Moderna. Successful expansion beyond melanoma could transform intismeran from a single new product opportunity into validation of Moderna's broader personalized cancer-vaccine platform.

Moderna Stock Offers Greater Upside — and Much Greater Risk

For Moderna, today's news potentially answers one of the biggest questions surrounding the company: Can its mRNA platform produce another major commercial franchise beyond respiratory vaccines?

The company generated only $145 million of revenue during the second quarter and posted a GAAP net loss of $800 million, or -$1.97 per share. Moderna nevertheless expects as much as 10% revenue growth in 2026 and projects ending the year with $4.7-$5.2 billion in cash and investments.

Based on Zacks estimates, Moderna’s annual sales are currently expected to rise over 7% this year to $2.09 billion, with its top line projected to expand another 23% in fiscal 2027 to $2.58 billion.

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Intismeran could dramatically change that fundamental picture. One analyst estimate cited following today's results sees potential melanoma sales reaching approximately $2.5 billion. Success in additional tumors would increase the opportunity considerably.

But investors are already paying aggressively for that possibility. Reaching a new 52-week high of $163 a share during Wednesday trading, Moderna stock carries a market capitalization of roughly $62 billion despite remaining unprofitable. Its valuation therefore depends far more heavily on future pipeline commercialization than current earnings power.

That makes MRNA the higher-upside but substantially higher-risk choice. Today's Phase 3 victory removes considerable clinical risk from intismeran, but regulatory approval, manufacturing individualized vaccines at scale, reimbursement, and expansion into additional cancers remain important hurdles.

Merck Has the Stronger Fundamentals

Merck presents almost the opposite investment case.

Keytruda is already one of the world's largest pharmaceutical franchises. Merck generated Q2 sales of $16.61 billion, up 5% year over year, while Keytruda and its newer subcutaneous formulation, Keytruda Qlex, generated $8.37 billion. Merck expects full-year 2026 revenues of $66.3-$67.3 billion or nearly 2% growth.

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Intismeran therefore represents incremental upside to an already highly profitable oncology platform rather than a company-defining binary event.

There is strategic significance as well. One of Merck's biggest long-term challenges is extending its oncology leadership as conventional Keytruda eventually faces patent-related pressures. A successful personalized vaccine paired with Keytruda could strengthen the franchise and potentially establish another major cancer platform.

Furthermore, Merck's valuation remains more conventional despite today's rally. At around $150 a share, MRK carries a market capitalization near $373 billion and now trades at 48x forward earnings, with an annual dividend yield around 2.5%.

That makes Merck's stock substantially easier to justify on existing fundamentals than Moderna's.

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MRNA or MRK: Which Cancer Vaccine Stock is the Better Investment?

Investors seeking maximum exposure to today's breakthrough will naturally gravitate toward Moderna. Intismeran could fundamentally reshape Moderna's long-term revenue trajectory, and positive results from other tumor types could create additional major catalysts.

However, following an intraday gain approaching 150%, much of that optimism is being capitalized immediately. Chasing such an enormous one-day biotech move before investors have seen the complete Phase 3 dataset carries considerable risk.

Merck looks more attractive for investors prioritizing fundamentals and valuation. Wednesday’s more than 10% jump is meaningful, but far less extreme, and buyers are acquiring an established pharmaceutical giant generating more than $60 billion in annual sales rather than primarily betting on future pipeline value.

Conclusion & Strategic Thoughts

Today's Phase 3 result is a landmark achievement for Moderna, Merck and the broader mRNA field. It substantially strengthens the investment case for both companies, particularly by validating personalized mRNA cancer immunotherapy at the late-stage clinical level.

Still, valuation matters after such explosive moves. Moderna offers greater upside potential if intismeran becomes a multibillion-dollar, multi-tumor franchise, but its enormous rally and continued losses make MRNA the more speculative stock. Merck provides a more balanced combination of established earnings, cash generation, dividends, and incremental cancer-vaccine upside.

Consequently, investors may want to avoid aggressively chasing either stock immediately following today's surge and wait for a more attractive entry point or additional Phase 3 details. Keeping that in mind, Moderna and Merck stock are both currently carrying a Zacks Rank #3 (Hold).

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This article originally published on Zacks Investment Research (zacks.com).

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