Limited humoral and cellular responses to Q fever vaccination in older adults with risk factors for chronic Q fever.

OBJECTIVES

In the Netherlands, people at risk for chronic Q fever were vaccinated against Coxiella burnetii with the inactivated whole cell vaccine Q-vax®. We aimed to measure the immune responses to C. burnetii six and twelve months after vaccination in this relevant population.

METHODS

In 260 vaccinees, antibody responses were assessed by immunofluorescence assay (IFA), complement fixation test and ELISA. The cellular immune responses were assessed by measuring C. burnetii-specific interferon (IFN)-γ production in blood. Serological results of 200 individuals with past Q fever were used for comparison.

RESULTS

At six months, 46% of vaccinees showed low IFA antibody titres and 67% had a positive IFN-γ assay; At twelve months, both were 60%. In contrast, individuals with a past Q fever were seropositive in 99.5% at six and twelve months, with relatively higher IFA titres. Interestingly, vaccinees with positive IFN-γ assay pre-vaccination, showed a higher seroconversion rate than IFN-γ negative vaccinees: 74% vs. 41% (p < 0.001).

CONCLUSIONS

The immune response after Q-vax® vaccination is lower and restricted to a smaller proportion than found after past Q fever and than previously described after vaccination, suggesting decreased vaccine immunogenicity in this high-risk population. A positive IFN-γ assay before vaccination in seronegative vaccinees likely points to pre-existing immunity resulting in boosting by vaccination.