July 7 (Reuters) - With U.S. approval of Eisai's and Biogen's Alzheimer's drug Leqembi secured, Wall Street analysts said they expect other region's health regulators to follow suit even if they share similar concerns about a potentially severe side effect.

Leqembi won standard approval from the U.S. Food and Drug Administration (FDA) on Thursday, but the FDA placed its strongest "boxed" safety warning on the drug's label, flagging the risk of potentially dangerous brain swelling in it and similar drugs.

Outside the United States, Eisai and Biogen are seeking approval for Leqembi, whose chemical name is lecanemab, in Japan, the European Union, China, Canada, Great Britain and South Korea.

A decision in Japan is expected by the end of September and in Europe within the year.

Ultimately, analysts expect Europe to approve the drug but said it was not a slam dunk. European experts told Reuters earlier this year they expect a cool reception to the drug.

Myles Minter, an analyst at William Blair, said the European Medicines Agency (EMA) tends to be more conservative than the FDA. As such, investors will be watching for the opinion of the agency's expert committee regarding the drug's safety, which comes ahead of the EMA decision, Minter said.

But he said he still expected approval. "We think (Europe's regulatory agency) will follow the FDA's suit and approve Leqembi later this year or early next year," he added.

Eisai disclosed the risk of brain swelling in its clinical trial data and it was discussed at an FDA meeting last month.

Shares of both companies fell on Friday, with Biogen down 3.4% or $9.80 at $275.34 in mid-morning U.S. trade, with analysts citing the safety warning as a negative surprise. Eisai fell 5% in Tokyo trade.

BMO Capital Markets analyst Evan Seigerman also expects the drug to be approved in Europe, but was unsure of the timeline. "At some point yes — but not sure when," he said, adding that other regulatory authorities could assign warnings to the drug that are the same, less restrictive or more restrictive.

However, Needham analyst Ami Fadia said it was difficult to interpret if Europe would follow suit. "I wouldn't say that EMA and FDA necessarily consistently follow exactly what the other is doing," Fadia said.

After the FDA approval and warning, most analysts stuck to their peak global sales estimates for the drug, some of which are above Eisai's own forecast of $7 billion by 2030.

Analysts forecast in research notes range from about $5 billion in 2034 at Canaccord Genuity to more than $14 billion by 2030 estimated at brokerage BMO Capital Markets.

William Blair estimated global sales of more than $8 billion in 2030, while brokerage Truist Securities expects more than $10 billion sales by 2035. (Reporting by Bhanvi Satija in Bengaluru, Additional reporting by Deena Beasley; Editing by Caroline Humer and David Holmes)