Evidence from mid‑2021 shows both in‑person conferences and U.S.–Europe leisure travel had resumed at clearly non‑trivial scale by summer 2021.

• In‑person conferences: Mobile World Congress 2021, one of the world’s largest tech trade shows, was held in Barcelona from June 28–July 1, 2021 as a hybrid event and drew about 20,000 in‑person attendees from over 100 countries, plus ~100,000 online participants.(icfo.eu) Coverage at the time described it as the first major tech convention to return physically, with organizers capping capacity around 35,000 but still calling the in‑person comeback a success and a springboard for more physical gatherings.(standard.co.uk) That level of attendance indicates conferences had resumed in a meaningful, not merely symbolic, way.

• International leisure travel (U.S. to Europe): By early June 2021, a long list of European countries—including Spain, France, Germany, Italy (via special flights), Greece, Denmark, Portugal, and others—had formally reopened for non‑essential / tourist travel from the U.S., usually for vaccinated Americans or those with negative tests.(traveloffpath.com) The EU as a bloc had also announced plans to reopen to fully vaccinated foreign tourists, specifically including Americans, by the start of summer 2021.(theguardian.com)

• Demand and volume indicators: A May 21, 2021 analysis by Hopper reported that, after the EU signaled it would allow vaccinated Americans in, searches from the U.S. to Europe jumped 47% in a day and 32% on a weekly basis, with strong clustering around July 4th weekend departures. It forecast higher transatlantic airfares driven by pent‑up demand and airlines adding capacity for summer 2021.(media.hopper.com) That behavior is consistent with a broad resumption of leisure trips, not just rare exceptions.

Conditions were still constrained compared to 2019 (capacity caps, testing/vaccine requirements, some big firms skipping conferences), but by any ordinary reading, large international conferences were happening again and Americans were vacationing in Europe in significant numbers by summer 2021. That matches Jason’s normalized prediction that “by summer 2021, in‑person conferences and international leisure travel (e.g., trips to Europe from the U.S.) will have resumed to a meaningful extent.”