The air in the nation’s capital is electric, and shirtless men in cuffed shorts are drunkenly spilling out of parks. But hanging over the party like a storm cloud is a recent rise in COVID-19 cases in the U.K.—three-quarters of which could be traced to the more infectious Indian variant, according to Public Health England.

Now, with the U.K. scheduled for a full end to COVID-19 era restrictions on June 21, the spread of the variant is giving investors cause for concern, analysts at Berenberg said.

The higher caseload of COVID-19 after a significant easing of restrictions— allowing Brits to hug, eat out, and go to the pub—is no surprise. But whether the U.K. is “on the cusp of another significant ‘third’ wave that would require renewed restrictions to contain the spread of the virus” has yet to be seen, Berenberg analysts note.

The U.K.’s beloved National Health Service currently faces no serious strain, with 870 patients in the hospital with COVID-19—down from 39,000 patients in mid-January. Cases are up 60% from two weeks ago, however, raising questions about whether the June 21 reopening date could be pushed back.

Scientists in the U.K. have also started to raise the alarm. Professor Ravi Gupta, a professor of clinical microbiology at the University of Cambridge and a member of a government advisory group on the virus, warned on the BBC Radio 4’s Today program on Tuesday that the U.K. is in the early stages of a third wave. Gupta called for a delay in the reopening, noting that although cases were “relatively low,” the Indian variant had already fueled “exponential growth.”

The game changer now will be how effective the U.K.’s pandemic rollout has been—and whether a new slate of cases either level off or rise without a material increase to hospitalizations and deaths. That would indicate that the virus is endemic—and manageable—much like the chicken pox. So far, both Pfizer and AstraZeneca have proven to be effective against the variant.

As of early June, nearly 39% of the U.K. population was fully vaccinated, and 59% have had at least one shot—putting the country slightly ahead of the U.S., as well as most European countries.

Crucially, low deaths and hospitalizations—even if cases rise—would also give other advanced economies the confidence to ease domestic and international restrictions with other safe countries, Berenberg analysts said.

The U.K. economy has been one of the hardest hit by the pandemic, with the Bank of England reporting the economy contracted 9.9% in 2020. It has since been recovering at a rate of 7% since the vaccine rollout began.

But if the U.K. can successfully sidestep the Indian variant, Berenberg, too, expects a celebratory summer for the U.K.—with an economic rebound analysts said could hasten a new “Golden Twenties.”