Summary: Greed prevented development of vaccine. - Merck Group acquired all the rights but didn’t work on them.

A cool thing you can do with Wikipedia is anchor links for sections like https://en.wikipedia.org/wiki/Marburg_virus#Vaccination

Or even in the case just link to

https://en.wikipedia.org/wiki/Marburg_vaccine

Edit

After reading through, what’s probably most important is

There is a candidate vaccine against the Marburg virus called rVSV-MARV. It was developed alongside vaccines for closely-related Ebolaviruses by the Canadian government in the early 2000s, twenty years before the outbreak. Production and testing of rVSV-MARV is blocked by legal monopolies held by the Merck Group. Merck acquired rights to all the closely-related candidate vaccines in 2014, but declined to work on most of them, including the Marburg vaccine, for economic reasons. While Merck returned the rights to the abandoned vaccines to the Public Health Agency of Canada, the vital rVSV vaccine production techniques which Merck had gained (while bringing the closely-related rVSV-ZEBOV vaccineinto commercial use in 2019, with GAVI funding) remain Merck’s, and cannot be used by anyone else wishing to develop a rVSV vaccine.