Emerging Diseases Lecture 8:

Polio

8.1: Overview8.2: Incidence and Timeline

8.3: The Vaccine RaceSalk Vaccine

Sabin Vaccine8.4: “Defeat” of Polio and the Age of

Optimism

8.1: Overview: Polio is an Ancient Disease

Poliomyelitis= polio

Caused by a virus- named poliovirus

Well-adapted to humans; Usually causes very mild disease

Less than 1/1000 paralytic

No other known hosts in nature

8.2: Disease Incidence

Polio has been present since the days of ancient Egyptians but was not a serious problem until recently.

As North America and Western Europe clean up their act in the late 19th and early 20th Centuries, incidence of most infectious diseases goes down.

But the incidence of polio goes up!????????

8.2: Polio Timeline in US1894: First US epidemic , in Vermont: 132 cases1916: Major outbreak nationwide: 9000 cases in

NYC alone1934: 2500 cases in Los Angeles1945-1949: at least 25,000 cases each year1952: 58,000 cases1953: 35,000 cases: “polio hysteria”-parents and

children terrified of polio

8.2: Why So Many Cases?

Disease very prevalent in human populations for many centuries.

Historically-age of exposure to contaminated water was very young-usually led to a mild childhood disease only.

Sanitation produces cleaner water.Delays age of first exposure. Severe symptoms more frequent in older

individuals.

Vaccine for Polio?• No cure for afflicted individuals• May lead to permanent paralysis-total or partial• Early attempts at vaccine in the 1930s went

terribly wrong• Scientists did not realize there were 3 strains of

the virus in circulation• By late 1930s National Foundation for Infantile

Paralysis/March of Dimes led the vaccine campaign

March of Dimes 1940s-50s an effective ad campaign

Salk Vaccine1948: Laboratory growth of poliovirus-use of cultured cells1950’s: Vaccine “race”1954: Large scale field trials of Salk (inactivated)

vaccine-small scale tests on Pittsburgh schoolchildren1955: April 12-successful vaccine announced1955: The Cutter Incident-Cutter Laboratories produce contaminated Salk vaccine1961: only 161 cases in US

Sabin Vaccine1962: Sabin (attenuated) vaccine approved aka oral polio vaccine = OPV1964: 121 cases in US

8.4: The “Defeat” of Polio

A folk memory in US todayBegins the “Age of Optimism”