Welch worked in New York for several months, living at the address of her future husband Thomas T. Mackie on Park Avenue before sailing in June 1940 to Puerto Rico.
Her destination in Puerto Rico was the School of Tropical Medicine in San Juan.

In 1941 Welch published a booklet, Nursing Education related to the Cultural Background in East and Southeast African Colonies.

Welch returned to England briefly during late 1941, leaving again on February 20, 1942 on board the SS Aircrest in an Atlantic convoy.
She entered the United States on March 2, and married Thomas Mackie on March 14.

As the Second World War intensified, Janet's husband was called into service.
He served as a doctor with the rank of Colonel, in the US Army in South East Asia.
Welch in the meantime continued to work in the US, publishing further booklets, including, Notes on the Techniques of Elementary Public Health Education in 1943 and contributing to publications such as The American Journal of Tropical Medicine and Hygiene: Adaptation of Public Health Practice to Foreign Cultures in 1944 and the American Journal of Nursing: Nursing in Other American Republics, 1945.
She travelled widely in Latin America during that time working for the US Office of the Coordinator for Inter-American Affairs.
There is at least one reference to her also working with Walt Disney on the series of public health and safety films that the studio produced during that time.

Reunited following the end of the war, Janet and Thomas were offered the opportunity to head up a new department at the Bowman Gray School of Medicine in Winston Salem, North Carolina.
She took up the post of assistant professor of preventive medicine in the spring of 1946.

Janet, became a US citizen in 1948.
In 1952, she left the school and became a medical consultant to the US Public Health Service.
Continuing to live in Winston Salem, Welch worked out of Washington DC, but she worked around the world, with developing communities both within and outside the US.
She is recorded as having been a US Public Health Service adviser in Thailand (1954) as well as with native American communities in the southwestern United States, Alaska and Hawaii.

By 1953, she was also a consultant to a World Health Organisation expert committee in Geneva.

Welch retired from the US Public Health Service in 1958, at the age of 64.
She continued to work with the WHO.
however, contributing to several publications and reports.

She also contributed a major section to the National Academy of Sciences publication Tropical Health which was published posthumously in 1962.

Janet Welch died on November 24, 1959.
She was waiting to board a train at Washington Union Station in Washington DC, heading home to Winston-Salem when she suffered a fatal heart attack.
She was buried at the Rock Creek Cemetery in Washington DC.
Welch worked in New York for several months, living at the address of her future husband Thomas T. Mackie on Park Avenue before sailing in June 1940 to Puerto Rico. Her destination in Puerto Rico was the School of Tropical Medicine in San Juan.
In 1941 Welch published a booklet, Nursing Education related to the Cultural Background in East and Southeast African Colonies.
Welch returned to England briefly during late 1941, leaving again on February 20, 1942 on board the SS Aircrest in an Atlantic convoy. She entered the United States on March 2, and married Thomas Mackie on March 14. 
As the Second World War intensified, Janet's husband was called into service. He served as a doctor with the rank of Colonel, in the US Army in South East Asia. Welch in the meantime continued to work in the US, publishing further booklets, including, Notes on the Techniques of Elementary Public Health Education in 1943 and contributing to publications such as The American Journal of Tropical Medicine and Hygiene: Adaptation of Public Health Practice to Foreign Cultures in 1944 and the American Journal of Nursing: Nursing in Other American Republics, 1945. She travelled widely in Latin America during that time working for the US Office of the Coordinator for Inter-American Affairs. There is at least one reference to her also working with Walt Disney on the series of public health and safety films that the studio produced during that time.
Reunited following the end of the war, Janet and Thomas were offered the opportunity to head up a new department at the Bowman Gray School of Medicine in Winston Salem, North Carolina. She took up the post of assistant professor of preventive medicine in the spring of 1946.
Janet, became a US citizen in 1948. In 1952, she left the school and became a medical consultant to the US Public Health Service. Continuing to live in Winston Salem, Welch worked out of Washington DC, but she worked around the world, with developing communities both within and outside the US. She is recorded as having been a US Public Health Service adviser in Thailand (1954) as well as with native American communities in the southwestern United States, Alaska and Hawaii.
By 1953, she was also a consultant to a World Health Organisation expert committee in Geneva.
Welch retired from the US Public Health Service in 1958, at the age of 64. She continued to work with the WHO. however, contributing to several publications and reports. 
She also contributed a major section to the National Academy of Sciences publication Tropical Health which was published posthumously in 1962.
Janet Welch died on November 24, 1959. She was waiting to board a train at Washington Union Station in Washington DC, heading home to Winston-Salem when she suffered a fatal heart attack. She was buried at the Rock Creek Cemetery in Washington DC.
Janet Welch