The Renaissance was a rediscovery of knowledge from ancient Greek and Roman times.
The Dissolution of the Monasteries by Henry VIII caused public health to decline as all hospitals run by monasteries were shut down. They were eventually replaced with free hospitals funded through charities with trained physicians that focused on recovery.
The influence of the Catholic Church decreased and Protestant Christianity became more popular across Europe. They lost authority and couldn't control medical training.
Dissection became an important part of medical training and research in stead of being outlawed by the Catholic Church.
New medical theories were able to spread and be pursued due to the invention of the printing press.
Galen's Teachings began to be questioned as attitudes changed due to the discovery of old knowledge.