(Bloomberg) -- Biotech giants Moderna Inc. and Amgen Inc. said they won’t attend JPMorgan Chase & Co.’s annual health-care conference in San Francisco in January, decisions that come as Covid-19 cases surge in the U.S. and the omicron variant poses a threat of increased transmission.

The event, known for its overcrowded panels and late-night parties, usually draws thousands to San Francisco’s Westin St. Francis hotel every winter. This year marks its 40th anniversary, and many industry players have been eager to return after last year’s event was forced online amid a winter surge in virus infections.

However, the recent climb in new Covid cases across the country, coupled with concern that omicron could add to those totals, has caused some industry leaders to call for holding the conference online again.  

The J.P. Morgan Healthcare Conference “should go virtual and avoid a super-spreader event and a PR disaster for our industry!” said John Maraganore, chief executive officer of Alnylam Pharmaceuticals Inc., in a tweet.

Moderna and Amgen, with market values of $110 billion and $120 billion, respectively, rank among the largest biotechnology companies in the U.S. 

Stat News first reported that the companies had pulled out of the event. Both Moderna and Amgen confirmed that they wouldn’t attend the conference in person, but didn’t elaborate on their decision-making process.  

Other drugmakers are weighing how to manage in-person events in coming weeks. Eli Lilly & Co. said that it was still planning to attend the JPMorgan conference, and the Indianapolis-based company plans to press on with an in-person investor event at the New York Stock Exchange on Wednesday. 

Pfizer Inc., Johnson & Johnson and Moderna Inc. didn’t immediately respond to request for comment. 

Read More: Who Has What? Omicron Raises Stakes for Quick Covid Sequencing

(Updates throughout with details on Moderna’s decision not to attend)

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