News that the inoculation developed by Pfizer Inc. and BioNTech SE was more than 90% effective in preventing Covid-19 infections sparked a flood of bets Monday on stocks such as cruise operators and airlines that have struggled during the pandemic. Refuges such as Treasuries, gold and the yen slumped.

But experts said the shot still has hurdles to clear, adding questions about its production, distribution and performance remain unanswered. That tempered the euphoric earlier embrace of a potential path out of the health crisis. Concerns about U.S. fiscal stimulus, the transition of power to President-elect Joe Biden and surging virus cases also came back to the fore.

Monday’s vaccine news was a positive and profound shock that “catalyzed a rogue wave of rotational optimism across global bond curves and risk-assets alike,” Edward Acton, rates strategist at Citigroup Inc., wrote in an email. However, he added “there’s a great deficit of information we’re facing when analyzing a post-vaccine landscape — with plenty of room for disappointment.”

A successful vaccine would shake up the prospects for the global economy. Yet some forecasters remain cautious about changing their outlooks without clarity on how quickly a shot can be rolled out. The pandemic continues to escalate in the U.S., Europe and elsewhere, with global cases now past 50 million.

While markets were surprised by the efficacy of the Pfizer inoculation, the “challenge from here is looking through rising virus cases, slowing data and perhaps less stimulus until a vaccine can be widely distributed in mid-2021,” Stuart Kaiser, equity-derivatives strategist at UBS Securities, said in an email.

The S&P 500 index closed at a two-month high on Monday, while the Nasdaq 100 index fell. Investors rotated out of defensive technology names into shares that would benefit if the pandemic ebbs. Principal Global Investors Chief Strategist Seema Shah wrote in a note that “market sentiment may be in the early stages of a burst of positive energy.”

Value shares — stocks trading at lower multiples to profits or book value — jumped globally. JPMorgan Chase & Co. strategist Marko Kolanovic said the vaccine news buttresses the case for the value rotation to endure.

Jim Vogel of FHN Financial said the reaction in bonds looked “appropriate,” while stocks seem “slightly ahead of themselves.” Sundial Capital Research Inc.’s Jason Goepfert noted that bursts of equity gains such as in the past week can often see a pullback as the moves are digested.

The vaccine-sparked global stock rally cooled Tuesday and havens such as gold and the yen clawed back some of Monday’s losses. S&P 500 futures edged up 0.1% of 8:40 a.m. in London.

Progress toward an inoculation could also have an impact on the timing and scope of fresh spending on U.S. pandemic relief, according to Michael Purves, chief executive officer at Tallbacken Capital Advisors LLC.

The “stronger the vaccine news becomes, it seems reasonable to assume that a Republican Senate will fight for a considerably smaller fiscal package the economy and the markets can count on,” he wrote in a note. That could wind up becoming a “considerable market vulnerability,” he added.