On a few occasions, special strips unrelated to the ongoing story have occured in daily and Sunday stories.
The Merry Christmas strips
In 1934, 1935 and 1937, special Merry Christmas strips were published in the dailies on December 25th.
A similar Merry Christmas strip was made for "The Phantom" in 1937. As a curiosity, Al Capp made Merry Christmas strips in 1947 to 1950 with wishes for merry christmas to many named people, including Lee and Connie Falk.
End World Hunger
In 1985 the Thanksgiving comics strips were peppered with reference to hunger, Africa and gluttony. The effort was organized by Garry Trudeau (Doonesbury), Charles Schulz (Peanuts) and Milton Caniff (Steve Canyon). The idea was to make a little more poignant message than a general reference to Thanksgiving, and give the readers the idea that it is an issue they should be concerned with. The Thanksgiving strips were later collected into a book, Comic Relief, and the book's proceeds were donated to USA for Africa. Each cartoonist dealt with hunger in their strips. Mandrake and The Phantom didn't interrupt the comic's story line but added the word End World Hunger to the bottom of one panel.
The Defenders of the Earth strip
The Sunday strips of Mandrake the Magician, The Phantom and Flash Gordon from September 28th 1986 were made as a promotional strip for The Defenders of the Earth series.
The Earth Day strips
In 2008 and 2009, special Earth Day strips were published in the dailies on April 22nd.