In 1963, the "epidemic" that was Beatlemania had seized Britain's teenagers. By Feb. 9, 1964, when John Lennon, Paul McCartney, George Harrison, and Ringo Starr made their American debut on The Ed Sullivan Show, the Beatlemania infection was going global.

Fans in Toronto scream during a visit by The Beatles on Sept. 7, 1964. | (Fox Photos/Getty Images)

Teenage girls were most susceptible to the pandemic and side effects included stamping, weeping, fainting, and screaming. When The Beatles played New York's Shea Stadium in 1965, The New York Times wrote of Beatlemania's unique sound: "[The crowd's] immature lungs produced a sound so staggering, so massive, so shrill and sustained that it crossed the line from enthusiasm into hysteria and soon it was in the area of the classic Greek meaning of the world pandemonium — the region of the demons."

The frenzy over the foursome is a phenomenon that is still unrivaled today. Join us on a brief tour of what Beatlemania would have looked like from The Beatles' perspective:

A tearful fan pleads with a policeman to deliver her fan button to Ringo, at an Indiana State Fair show in Indianapolis on Sept. 4, 1964. | (AP Photo/Bob Daugherty)

New York City, Aug. 27, 1964. | (WATFORD/Mirrorpix/Corbis)

Seattle Center Coliseum on Aug. 24, 1964. | (William Lovelace/Express/Getty Images)

New York City, circa 1964. | (Keystone/Getty Images)

Ernst-Merck-Halle in Hamburg, Germany, on June 26, 1964. | (AP Photo/Heinz Ducklau)

Seattle Center Coliseum on Aug. 24, 1964. | (William Lovelace/Express/Getty Images)

Welcoming The Beatles as they arrive in New York City in February 1964. | (Keystone/Getty Images)

The audience at the The Ed Sullivan Show on Feb. 9, 1964. | (Central Press/Getty Images)

Comiskey Park in Chicago on Aug. 20, 1965. | (Bettmann/CORBIS)

A concert in Philadelphia on Aug. 16, 1966. | (AP Photo)