“We all expect a major new surge from Omicron or a new variant in the global south from June to September, and if that happens, we are not going to be ready with test and treat,” said Dr. Bill Rodriguez, who runs the testing arm of the ACT Accelerator, the Geneva-based consortium coordinating the global response. “It feels extremely similar — painfully, ironically, tragically similar — to what happened with H.I.V.”

On Monday, ahead of the summit, the consortium, which is backed by the World Health Organization, is set to convene a discussion of global health experts and declare access to testing and treatment an “equity issue,” officials said.

Mr. Biden may well show up at his own summit empty-handed. The White House has asked Congress for an additional $22.5 billion in emergency coronavirus aid, including $5 billion for the global response, but Senate Republicans are refusing to authorize any funding unless it is offset by cuts to other programs. A $10 billion compromise proposal includes no money for the global response, and it is unclear when or whether that plan will come up for a vote.