The acquisition of a substantial stake by a major pharmaceutical company like Merck & Co is typically viewed as a positive endorsement of the smaller company's potential, leading to increased investor confidence and a likely short-term rise in stock price.

While the stake in Evaxion Biotech is a notable investment for Merck, it is less likely to have a significant short-term impact on Merck's stock price due to its larger market capitalization and diversified portfolio.