• Vaccine Name: M-44
• Target Pathogen: Coxiella burnetii
• Target Disease: Q fever
• Vaccine Ontology ID: VO_0004131
• Type: Live, attenuated vaccine
• Preparation: Crude rickettsial pools are produced in embryonated eggs of hens free from avian leucosis virus. The embryonated eggs are inoculated with 0.2 ml of seed stock containing 10^7.9 median infectious doses at 35C. After 6 to 7 days, the yolk sacs are collected and diluted to a 50% suspension with distilled water. The strains are then obtained through purification using alternating low-speed and high-speed centrifugations. After centrifugation, the pellet is suspended in 10% sucrose and centrifuged onto a 70% sucrose solution. The purified strains are then obtained from the surface and diluted with Snyder I buffer to result in a final titer of 10^9.5 median infectious dose per ml and freeze-dried (Robinson and Hasty, 1974).
• Description: M-44 vaccine is developed from attenuated phase II M-44 strain of C. burnetii (Robinson and Hasty, 1974).

Guinea pig Response

• Host Strain: Hartley guinea pigs
• Vaccination Protocol: Hartley guinea pigs (250 to 350 g) were immunized intraperitoneally or subcutaneously with serial 10-fold dilutions (prepared in physiological buffered saline) of M-44 vaccine (Robinson and Hasty, 1974).
• Immune Response: Vaccine at high doses prevented anamnestic-type response (Robinson and Hasty, 1974).
• Challenge Protocol: Guinea pigs were challenged with either phase I or phase II C. burnetii (Robinson and Hasty, 1974).
• Efficacy: 10^2 median infectious dose protected the guinea pigs from death, but did not protect the animals from febrile effects of challenge. Protections against the febrile effects of the challenge of phase I C. burnetii were observed at vaccines doses of 10^4 median infectious dose or greater. Protections against the febrile effects of the challenge of phase II C. burnetii were observed at vaccine doses of 10^3 median infectious dose or greater (Robinson and Hasty, 1974).