Eastern Europe had to continue with phage therapies because they didn't have great access to antibiotics, which have many superior properties. Phage was used in the Western world, but early versions had serious purification issues, where people were getting killed by bacterial endotoxins present in the solutions.
It's not really "lost" as much as a readily obvious alternative was present in one setting and not the other.
> Eastern Europe had to continue with phage therapies because they didn't have great access to antibiotics […]
This is a very bubble centric view of the history. Eastern bloc countries, notably East Germany, Hungary and Yugoslavia, had very active and thriving drug research and manufacturing sectors. The Soviet Union, whilst having the drug research and manufacturing of their own, was purchasing swaths of drugs from the three aforementioned countries.
Azithromycin, one of the most widely prescribed macrolide antibiotics in the US today, was, in fact, discovered in Yugoslavia and licenced to Pfizer in 1980s.
Phage therapy was considered a novel area of research in a few of the Eastern bloc countries, but it never became neither widespread nor a substitute for antibiotics. It was just as fringe in those countries as it was elsewhere.
Eastern Europe had to continue with phage therapies because they didn't have great access to antibiotics, which have many superior properties. Phage was used in the Western world, but early versions had serious purification issues, where people were getting killed by bacterial endotoxins present in the solutions.
It's not really "lost" as much as a readily obvious alternative was present in one setting and not the other.