In 1943, the mass production of penicillin for clinical use was begun. This occurred after researchers “discovered” Fleming’s writings, and approached large pharmaceutical companies. Penicillin soon became readily available to Allied troops during World War II.

Penicillin proved highly effective on D-day, and saved countless lives.

The use of penicillin became widespread, and it was generally believed that the end of bacterial infections was near. The antibiotic was effective, saved lives, and was given to patients undergoing surgery to prevent infection.

As spectacular as the results at the end of World War II were, resistance to the new drugs arose with sudden, and at the time, unappreciated rapidity. Once mass production of penicillin was introduced, it took only three years for the staphylococcus species of bacteria to develop the ability to grow in the presence of penicillin.

The first cases were discovered in London in 1943 by Mary Barber. Looking back in 1961 in a review entitled “Hospital Infection Yesterday and Today,” she noted that

“By 1946, however, they (sic penicillin resistant staph) were becoming quite frequent, and a few years later, in hospitals all over the world, they outnumber penicillin sensitive strains… Today penicillin resistant staphylococcal infection is common even in hospital outpatients.”

By the late 1940s, antibiotics including streptomycin, tetracycline, and erythromycin were developed. Methicillin was discovered in the 1960s, as was Vancomycin, a drug that remains a “drug of last resort” in treating severe infections that are unresponsive to other antibiotics.

After the 1960’s development of new antibiotics slowed, due to the combination of tighter regulations resulting from new safety laws and a desire to hold new antibiotics in reserve. Currently the “time to resistance” for a newly introduced antibiotic remains at around 18 months.

As antibiotics are only effective against bacteria, vaccines were developed to target viruses, including smallpox, measles, mumps, typhoid fever, rubella, diphtheria, tetanus, yellow fever, pertussis, and poliomyelitis. Advancements in antiviral drugs were made starting in the 1970s with the introduction of acyclovir to protect against herpes and cold sores.