It was from a pan full of engorged, doubly-infected ticks like the one shown here that Spencer decided to try to make a vaccine with by grinding the ticks with phenol (also known as carbolic acid, a strong disinfectant). He injected the ground-up ticks into healthy guinea pigs to vaccinate them. Then he infected both the vaccinated guinea pigs and unvaccinated guinea pigs with RMSF; the vaccinated guinea pigs did not get sick, while unvaccinated ones died.

“The feasibility of human vaccination also naturally arises,” he wrote in his 1924 paper describing these studies. And he adds that he tried the vaccine on one human, with no ill effects. The human was himself.

(Quote: "Rocky Mountain Spotted Fever: Experimental Studies on Tick Virus" Roscoe R. Spencer and Ralph R. Parker, Public Health Reports, Vol. 39, No. 48, November 28, 1924, pp. 3027-2040) 1.3 MB

This bottle of Rocky Mountain spotted fever vaccine from the early 1940s represents much scientific work and practical experimentation. There were no strict research protocols for vaccine development and testing in the early 19^th century. There was no oversight or approvals from the Food and Drug Administration. The Hygienic Laboratory (NIH’s precursor) had regulatory authority, testing commercial vaccines for safety and effectiveness. Spencer worked at the Hygienic Laboratory and was certainly familiar with the tests required to prove that a vaccine worked safely and at what dose it should be given, as well as the standards for producing a safe vaccine. He knew proving that his RMSF vaccine worked would take more than inoculating himself with it.

After experimenting with different combinations of fed vs. unfed ticks and ticks in different stages of their life cycle to get the highest concentration of RMSF in the vaccine, Spencer and Parker were ready for the next step.  In February 1925, they conducted an experiment in 18 monkeys to see if the vaccine was effective and safe. None of the vaccinated monkeys died; all of the unvaccinated monkeys did.

Next was to test the vaccine on people, and the Canyon Creek Schoolhouse laboratory staff became the participants in this early clinical trial. Thirty-four laboratory and field workers were vaccinated, and none had a severe reaction.

There were questions about the vaccine: what was the optimum dose? How long did immunity last? And how long did it take to gain immunity after being vaccinated? That last question was answered in April 1925, when a cattle-dipper for the Montana State Board of Entomology was vaccinated. He came down with RMSF a few days later but recovered. Four other people in the Bitterroot Valley who also got RMSF at the same time, but had not been vaccinated yet, all died. From this unplanned experience, Spencer and Parker learned the time required to gain immunity after vaccination: 10 days.

Giving Vaccinations

After using the Canyon Creek Schoolhouse laboratory staff as an informal clinical trial, vaccination trials of the people most exposed to RMSF were begun. These trials focused on people most likely to get RMSF because of their jobs, such as shepherds and cattlemen. These shepherds in Idaho received their shots in 1926.   

In this photo, vials of the Spencer-Parker RMSF vaccine sit on the letter or telegram requesting the vaccine from places all over the United States. The Canyon Creek Schoolhouse laboratory was producing as much of the vaccine as possible, but demand for the vaccine exceeded the supply, making the construction of a new building designed specifically for scientific research and vaccine production necessary—Building One of the present Rocky Mountain Laboratories campus in Hamilton, Montana.