Amazing medical advances discovered by accident

By Naveed Saleh, MD, MS
Published August 7, 2020

Key Takeaways

Serendipity plays a larger role in science than most people likely realize. In fact, there are four types of serendipity in science, as categorized by onetime biochemist turned social scientist Ohid Yaqub, PhD, MSc:

1. Instances when one discovery leads to another, such as the cause of mustard-gas explosions leading to the idea of chemotherapy. 

2. Occasions when an untargeted search leads to innovation, as with X-rays, the discovery which is detailed below. 

3. Discoveries that result when a desired solution arises from an unexpected path, such as the process of vulcanizing rubber. 

4. Serendipitous discoveries that answer a problem that only later comes to light, such as the discovery of shatterproof windshields that arose from observations involving a fallen laboratory flask.

The following are five notable examples of serendipity in medicine.

Smallpox vaccination

In 1796, after a chance encounter, a British surgeon named Edward Jenner was told by a young milkmaid that people who were infected with cowpox, a relatively harmless illness spread from cows to humans, never developed smallpox.

Dr. Jenner was inspired to take specimens from open cowpox sores from a young dairymaid and inoculated an 8-year-old boy with them (a step that would definitely be thwarted by institutional review boards of today.) The boy manifested a mild fever and a few lesions, but was otherwise healthy. Months later, Dr. Jenner injected the boy with smallpox. The boy did not fall ill, and the first vaccination came to light.

Although it would be more than half a century before scientists elucidated the theoretical underpinnings of vaccination, in this iteration, smallpox vaccination became popular and effective worldwide soon after its discovery.


As with the smallpox vaccination, warfarin was an accidental discovery that involved cows. In the 1930s, the American biochemist Karl Paul Link, PhD, encountered a Wisconsin farmer who complained that his cows were experiencing unexplained bleeding. After examining the cattle’s feed, Dr. Link noted that an anticoagulant was present. He isolated the compound, warfarin, which has been used ever since to treat clotting.

Pap smear

In 1923, George Nicholas Papanicolaou, MD, was examining vaginal fluid from women with the intention of observing cellular changes that occur during the menstrual cycle. He had already noted such cell transformation in guinea pigs and hoped to see similar results in humans.

In a eureka moment, he noticed that cancerous cells were clearly identifiable when he examined a smear from a woman with uterine cancer. Thus, the Pap smear was born—a revolutionary way to test for early signs of uterine cancer.


X-rays are ubiquitous in medicine and used to help diagnose a gamut of pathology from fractures to heart failure. 

In 1895, Wilhelm Roentgen, a German professor of physics, was testing whether cathode rays could penetrate glass. By accident, he discovered that an incandescent green light that emitted from the cathode ray tube could pass through most things, but leave shadows of solid objects. He called the rays “X” for “unknown.”

Roentgen soon discovered that X-rays could penetrate the body and leave shadows of bones and tissue. Within a year, physicians in the United States and Europe were using X-rays to identify fractures, gunshots, swallowed objects, kidney stones, and more. For his work with “roentgenograms,” Roentgen received the first Nobel Prize in physics in 1901.

Intraocular lenses

Cataracts are the most common cause of blindness. For a long time, the only treatment was to push the clouded lens out of the way with a needle, a highly painful procedure called couching. Alternatively, the clouded lens could be removed, as demonstrated in 1747 by a French ophthalmologist, but this procedure was also far from optimal.

As a newbie ophthalmologist in 1930s England, Harold Ridley first thought of replacing clouded natural lenses with artificial ones. His mentor, however, rebuffed this hypothesis. It wasn’t until Gordon “Mouse” Cleaver, an ace World War II pilot in the Royal Air Force, sustained eye injury that proof-of concept for Dr. Ridley’s idea emerged.

In 1940, Cleaver’s airplane was peppered with machine-gun fire, which caused the craft to go up in flames. Cleaver forgot to wear his goggles and shards of acrylic from the acrylic canopy lodged in both his eyes. Fortunately, the pilot parachuted to safety, but the damage to his eyes was severe in addition to suffering severe burns. He lost sight in his right eye and needed numerous surgeries to his left eye to save some of his vision.

Dr. Ridley examined the war hero on several occasions and noted that, although causing physical damage to the lenses, the acrylic that lodged in the pilot’s eye was not rejected by the body. In 1949, Dr. Ridley successfully implanted the first intraocular lens. The breakthrough, however, was overlooked until the 1980s, when the procedure was widely embraced as a way to treat cataracts. 

Dr. Ridley was eventually honored by being elected to the Royal Society in 1986. Ironically, Mouse Cleaver received an intraocular lens implant to treat his cataract in 1987.

Share with emailShare to FacebookShare to LinkedInShare to Twitter