I want to know the answer to the following question:
What compound made the diphtheria vaccine safer to use?
All the background I'm provided with is that "In 1923 parallel efforts by Gaston Ramon at the Pasteur Institute and Alexander Glenny at the Wellcome Research Laboratories (later part of GlaxoSmithKline) led to the discovery that a safer vaccine could be produced by treating diphtheria toxin with formaldehyde.". Is that enough to answer the question?
Answer: yes