Harper grew up in Kansas City; her father was an electrical and mechanical engineer. Her mother, who was from Missouri, died in July 1981 of breast cancer.
A graduate of the University of Kansas (where she completed a residency in family medicine), Harper also completed undergraduate and graduate degrees at the Massachusetts Institute of Technology in chemical engineering, her original choice of major, before attending Stanford University and Harvard University to receive her public health degree. Her decision to go to medical school instead of continuing to study engineering was made in 1981, when, on Thanksgiving Day, she called her dad and told him that her heart wasn't in engineering. While at Stanford, she studied medical decision making and cost-effectiveness analysis. Harper's degrees include MD, MPH, and MS.
Harper has co-authored clinical trials of HPV vaccines in journals including the New England Journal of Medicine and The Lancet Oncology.
Although, in 2008, she stated that Gardasil "is a good vaccine and ... is generally safe," in recent years, mainly beginning in 2009, Harper has questioned the safety of Gardasil, and has appeared at the International Public Conference on Vaccination, a conference held by the National Vaccine Information Center, a U.S. nonprofit group that has consistently advocated against the use of vaccines. She also appeared in The Greater Good, an anti-vaccine film.
Pointing to research by Barbara Slade, Harper states, "Gardasil has been associated with at least as many serious adverse events as there are deaths from cervical cancer developing each year. Indeed, the risks of vaccination are underreported in Slade's article, as they are based on a denominator of doses distributed from Merck's warehouse. Up to a third of those doses may be in refrigerators waiting to be dispensed as the autumn onslaught of vaccine messages is sent home to parents the first day of school. Should the denominator in Dr. Slade's work be adjusted to account for this, and then divided by three for the number of women who would receive all three doses, the incidence rate of serious adverse events increases up to five fold."
In October 2009 Harper stated to the Guardian "I fully support the HPV vaccines," she says. "I believe that in general they are safe in most women."
In the December 2009 issue of Current Opinion in Obstetrics and Gynecology, Harper published an opinion piece regarding the potential risks of both Gardasil and Cervarix, and concluded that, given the various limitations and risks of the vaccines, the beneﬁts and risks of HPV vaccination must be weighed with the beneﬁts and risks of HPV screening (Pap smears) to reduce cervical cancer in a cost-effective manner. This paper was challenged by two scientists from Merck (the maker of Gardasil), who wrote, among other things, that it "contains inaccuracies and assumptions not supported by the currently available data" and that its methodology was flawed because "Efficacy estimates alone cannot be compared across studies and populations in order to infer differences in vaccine impact."
In a 2011 NPR interview, she argued against mandatory HPV vaccines for schoolchildren, saying "Ninety-five percent of women who are infected with HPV never, ever get cervical cancer." In an article in the 2013 book Vaccination Controversies: A Reference Handbook, she argued further against HPV vaccine mandates for schoolchildren, because "Population health models show that if the HPV vaccine does not last for at least 15 years, no cancers will ever be prevented; women will just get the cancers at a later time in life after the vaccine has worn off" and that Gardasil and Cervarix have only been shown to last for 5 and 9.4 years respectively. In 2012 she told Women's Health that "[I]t's critical to note that more than 70 healthy young girls have died from a neurological reaction that occurred soon after getting Gardasil; you can avoid the risks by opting for a lifetime of Pap smear screening rather than vaccination." In a July 2013 interview, she stated that she advocates personal choice and an individualized approach to HPV vaccination, saying that she provides "a balanced picture to my patients and their families and am not at all upset if they refuse the vaccine, especially at younger ages." Harper appeared on a December 2013 episode of Katie Couric's show Katie devoted to the HPV vaccine, and stated that newly developed pap screenings that combine HPV testing and cytology have a nearly 100% ability to detect pre-cancers and cancers; she noted that Gardasil doesn't last long enough to prevent cervical cancer and that there are some harms associated with it.
In 2006, while she was on the faculty and staff of Dartmouth Medical School, the New Hampshire Academy of Family Physicians named Harper the New Hampshire Family Physician of the Year.
In May 2013 Harper received the Prix Monte-Carlo Woman of the Year award in Monte Carlo for her contributions and discoveries defining the role of HPV in the pathology of cervical cancer.
In May 2013 Harper also received the Society of Teachers of Family Medicine Excellence in Education Award for her "excellence in education at every level from medical students, family medicine residents, residents in obstetrics and gynecology, national and international meetings, and to the public and national audiences via television, including an appearance on the Dr Oz show ...." The award also noted that Harper "helped establish the US national guidelines for the nomenclature of cytology and the screening and management of abnormal cytology and histology reports" and "consulted for the World Health Organization on the use of prophylactic HPV vaccines".
In October 2015, Dr. Harper was named the Alum of the Year by the Notre Dame de Sion School system.
In 2016, Dr. Harper was appointed to the United States Preventive Services Task Force.Harper, Diane M.; DeMars, Leslie R. (July 2017), "HPV vaccines – A review of the first decade", Gynecologic Oncology, 146 (1): 196–204, doi:10.1016/j.ygyno.2017.04.004