MRK’s Enflonsia—like SNY’s Beyfortus—is a monoclonal antibody that’s given prophylactically to infants during their first RSV season. These drugs are effective at preventing RSV temporarily, but they are neither vaccines nor treatments for an active infection. Hence, most patients who receive Enflonsia or Beyfortus end up getting an RSV infection during their second or third season (when the prophylactic value of these antibodies has long since vanished).
In other words, Enflonsia and Beyfortus do not materially eat into the addressable market for ENTA’s RSV treatments.
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