Counting sheep: Louis Pasteur and the first registered public vaccine trial

During the COVID-19 pandemic, vaccine development took center stage in the media and minds of the global community. This same daily scrutiny was also applied to the first public registered vaccine trial of anthrax prevention among livestock led by French scientist Louis Pasteur in 1881. At a meeting with the president of the Agricultural Society of Melun, Pasteur outlined what might be considered the first "registered" vaccine trial protocol. The trial proposed a three-arm trial where anthrax-naïve sheep (n = 60) and cows (n = 10) would be assigned either to a treatment group consisting of a 2-dose anthrax vaccination in addition to an anthrax challenge, a control group consisting of an unvaccinated group given the anthrax challenge or a second control group which received neither vaccine nor anthrax challenge. All vaccinated sheep and cows were alive 48 h post-challenge. All unvaccinated sheep who received the anthrax challenge died within 48 h post-challenge, and the unvaccinated cows developed large edemas at the site of inoculation. Witnessing the 100% efficacy of Pasteur's vaccine were hundreds of, mostly skeptical, onlookers including journalists who disseminated the big news across Europe within days. Two months later, the results of the trial reached North America, via attendees who had heard Pasteur's address at the International Medical Congress in London in August 1881. Pasteur's anthrax vaccine trial laid the foundations for the systematic, public, and a priori reporting of clinical trial procedures and codes of conduct which developed into the registered clinical trial protocols of today.