In 1966, 103 cases of paralytic poliomyelitis were reported in the United States. An outbreak of 66 cases caused by type 1 poliovirus occurred in Texas, predominantly in unimmunized, preschool children. In 1967, 40 cases were reported, with 16 in southwestern border states. In both years, sporadic cases of poliomyelitis continued to occur in persons without known contact with either live oral poliovirus vaccine, or with other patients. During the three-year period 1965-1967, eight cases of paralytic poliomyelitis occurred in recent recipients of oral poliovirus vaccine, while 16 additional cases were reported in persons with familial or other close contact with vaccine recipients. In view of the proven benefit of oral poliovirus vaccines, however, these cases present a minor public health problem.
Hopkins CC, Dismukes WE, Glick TH, Warren RJ. Surveillance of Paralytic Poliomyelitis in the United States1966 and 1967 Cases, and 1965-1967 Cases Associated With Oral Poliovirus Vaccine. JAMA. 1969;210(4):694-700. doi:10.1001/jama.1969.03160300034006