Heating at 37° C. for 5 days completely abolished the capacity of a trachoma/inclusion conjunctivitis (TRIC) vaccine to protect baboons against conjunctival infection. Treatment with formalin also impaired or abolished immunogenicity.
The rate of inactivation of TRIC agent by ultraviolet light was exponential, and was about 7 times faster than that of a suspension of vaccinia virus of comparable turbidity. By contrast with vaccinia, irradiation of TRIC agent with twice the dose of ultraviolet light needed to destroy infectivity resulted in loss of immunogenicity.
The deleterious action of these inactivation procedures on the potency of TRIC vaccines may be explained in terms of damage to a protective antigen; alternatively, live vaccines may be more immunogenic because TRIC agents are capable of multiplying within primate hosts after parenteral injection.
Unlike the same type of variant of another strain of inclusion conjunctivitis, the ‘fast-killing’ variant of MRC-4 was still pathogenic for the baboon conjunctiva.