Shares of the vaccine maker Moderna (MRNA) are up by double digits in after-hours session Tuesday, thanks to a positive clinical update for its experimental coronavirus vaccine mRNA-1273. “Phase 1 data demonstrate that vaccination with mRNA-1273 elicits a robust immune response across all dose levels and clearly support the choice of 100 µg in a prime and boost regimen as the optimal dose for the Phase 3 study,” said Tal Zaks, Chief Medical Officer of Moderna.Following Moderna’s massive gains so far this year, 333% to be exact, is now the right time to recommend investors snap up shares? Jefferies analyst Michael Yee has an almost Schwarzenegger-ish answer to such a question: “We take a stand: If it works, stock will be going up.”To this end, Yee initiated coverage on MRNA with a Buy rating. However, his $90 price target implies a modest 5% upside from current levels. (To watch Yee’s track record, click here)Unsurprisingly, the bulk of Yee’s bullish assessment is reserved for the company’s COVID-19 vaccine candidate.Expanding on this blunt assessment, Yee said, “We believe the Street will be surprised to the upside if the COVID-19 vaccine works, gets approved by early 2021, and there are multi-billion dollars of purchase orders from USA and around the world. The Street is divided as to what will happen or if the vaccine will even work and is hugely divided on valuation. We believe the vaccine will get approved and could do $5B+ in orders over the next few years and the stock will head higher.”Yee’s confidence is partly based on talks with KOLs (key opinion leaders) who have prompted a belief there is “a good probability the vaccine will work,” and should at minimum be granted Emergency approval by early next year.Moderna has emerged as one of the frontrunners in the race to bring a viable vaccine to market, but there’s a while to go yet before breaking out the champagne. mRNA-1273 is currently in a phase 2 trial, with data expected in the fall, while a phase 3 study is expected to launch this month. It goes without saying, positive results from the trials could act as additional catalysts for further share appreciation.The Jefferies analyst is not alone in his positive assessment. Based on 14 Buy ratings and 2 Holds, Moderna has a Strong Buy consensus rating. With an average price target of $86.46, the analysts expect a 15% premium to be added to the share price over the next 12 months. (See Moderna stock analysis on TipRanks)To find good ideas for healthcare stocks trading at attractive valuations, visit TipRanks’ Best Stocks to Buy, a newly launched tool that unites all of TipRanks’ equity insights.