NEW YORK, Nov 30 (Reuters) - The emergence of a worrisome coronavirus variant is benefiting shares of vaccine makers Moderna Inc (MRNA.O), BioNTech and Pfizer (PFE.N) as investors search for winning bets in markets roiled by uncertainty in recent days. Moderna shares have jumped 28% since last week when the variant, named Omicron, triggered global alarm. Shares of vaccine partners Pfizer and BioNtech have also climbed over that time, with Pfizer up 6% and U.S. shares of BioNTech jumping 15%, in contrast to a decline in the S&P 500 (.SPX) of 2.5%.Moderna and Pfizer/BioNTech are the predominant vaccines used in the United States, and it is expected they will be able to re-engineer their products to address the new variant if required. “They are clear COVID plays and anything that ramps up the intensity of COVID is going to benefit them," said Kevin Kedra, pharmaceuticals analyst at GAMCO Investors. "They are the front line of defense against COVID.” Along with the rise in vaccine stocks, the market reactions to the new variant included a sell-off in travel and leisure stocks and brief increases in stay-at-home stocks that thrived during lockdowns in 2020. read more The companies have already reaped enormous profits from their vaccines, juicing their stock prices this year. Moderna shares are up 240%; shares of Pfizer, which also is seeking emergency authorization for its experimental antiviral COVID-19 treatment, are up 47%, while BioNTech has seen a 340% gain.Buying vaccine stocks is part of "a playbook that we have learned over the last 18 months, give or take. I think it is more mechanical than thoughtful,” said Les Funtleyder, a healthcare portfolio manager at E Squared Capital. “We don’t have all the information. People are jumping the gun," Funtleyder said. "They may be making the right choice, but we are not going to know for a little while." Much remains uncertain about Omicron, including how contagious it is, whether it will cause more severe disease than other variants and how protective existing vaccines are against it. read more The head of Moderna, Stéphane Bancel, said vaccines are unlikely to be as effective against Omicron as they have been against previous variants, while BioNTech"s chief said the company"s vaccine would likely offer strong protection against any severe disease from the new variant. read more Kedra said Bancel"s comments may have been one factor weighing on shares of Moderna and BioNTech on Tuesday. Moderna was down 5% and BioNTech was down 3%. Pfizer"s shares were up 3.5% Tuesday. Analysts have been scrambling to assess the business implications from the new variant. “It seems much more likely that we are going to have at least one more round of boosters," said Daina Graybosch, senior research analyst at SVB Leerink. Jefferies analyst Michael Yee said in a note that the "emergence of Omicron represents an increase in need for continued protection against COVID-19 and its variants through the use of primary vaccination for some, and administration of boosters for many." The emergence of Omicron has also reverberated through shares of makers of treatments for COVID-19. Vir Biotechnology (VIR.O), which said its antibody therapy will likely maintain potency against the variant, has seen its stock rise some 45% since last week. read more Shares of Adagio Therapeutics (ADGI.O) have soared 130% in volatile trading over that time. The company said it expects its experimental antibody therapy will retain activity against Omicron. Regeneron Pharmaceuticals (REGN.O) said on Tuesday its antibody drug could be less effective against Omicron and was doing further study to quantify the potential impact using the variant"s genetic sequence. Regeneron shares have fallen 1% since Omicron emerged.