Vaccine hesitancy, also known as anti-vaccination or anti-vax, is a reluctance or refusal to be vaccinated or to have one’s children vaccinated against contagious diseases. It was identified by the World Health Organization as one of the top ten global health threats of 2019.^[1][2] The term encompasses outright refusal to vaccinate, delaying vaccines, accepting vaccines but remaining uncertain about their use, or using certain vaccines but not others.^[3][4] Arguments against vaccination are contradicted by overwhelming scientific consensus about the safety and efficacy of vaccines.^[5][6][7][8]

Hesitancy primarily results from public debates around the medical, ethical and legal issues related to vaccines. Vaccine hesitancy stems from multiple key factors including a person’s lack of confidence (mistrust of the vaccine and/or healthcare provider), complacency (the person does not see a need for the vaccine or does not see the value of the vaccine), and convenience (access to vaccines).^[4] It has existed since the invention of vaccination, and pre-dates the coining of the terms “vaccine” and “vaccination” by nearly 80 years. The specific hypotheses raised by anti-vaccination advocates have been found to change over time.^[9] Vaccine hesitancy often results in disease outbreaks and deaths from vaccine-preventable diseases.^{[10][11][12][13][14][15]}

Bills for mandatory vaccination have been considered for legislation, including California Senate Bill 277 and Australia’s No Jab No Pay, all of which have been strenuously opposed by anti-vaccination activists.^[16][17][18] Opposition to mandatory vaccination may be based on anti-vaccine sentiment, concern that it violates civil liberties or reduces public trust in vaccination, or suspicion of profiteering by the pharmaceutical industry.