Influenza Vaccine in Lung Transplant Patients - Antibody

Lung transplant patients may be at an incrementally higher risk of influenza infection than other transplant patients. Factors that predispose them to respiratory infection include high degree of immunosuppression, altered mucociliary clearance, repeated airway instrumentation, bronchial anastomotic obstruction, disruption of lymphatic drainage, and the exposure of the transplanted organ to the environment.

The influenza vaccine used for those at high risk for influenza morbidity and mortality is an inactivated trivalent preparation. Influenza vaccine contains 2 type A viruses and 1 type B virus. The vaccine is reformulated each year based on the viruses expected to circulate during the upcoming season. A protective antibody response to influenza vaccine is considered an antibody titer of at least 1:40. Seroconversion following influenza immunization implies at least a 4-fold increase in antibody concentrations. Although these indicators of a positive response to influenza immunization have significant overlap, they are not exactly the same. One must consider that a person may have antibodies before immunization because of previous exposure to a vaccine virus or an antigenically similar influenza strain.

Seroconversion rates following influenza vaccination are lower in lung transplant patients than in healthy persons. Clearly, immunization elicits an antibody response in this population, but the response is not as vigorous as in immunocompetent persons. It has been demonstrated that only the B/HongKong virus was associated with a lower seroconversion rate, and this virus was the only one to change from the previous year's vaccine. Seroconversion rates decrease with subsequent exposure to the same influenza vaccine viruses, but seroprotection rates remain the same. It is conceivable that the seroconversion response is more affected by immunosuppression than is the seroprotection response. Stated another way, the ability to mount a high spike in antibody production is hindered. It is difficult to fully ascertain the exact degree of immune impairment in lung transplant recipients because both studies investigating influenza vaccine response used healthy persons as the comparison group. Healthy persons may have less experience with influenza vaccine than do persons with severe respiratory conditions. An immunologically naive host is more likely to mount the large change in antibody concentration and increase the likelihood of seroconversion. Therefore, patients waiting for lung transplantation were used as a comparison group.

This prospective, parallel study was done to investigate the responses to influenza vaccine in consecutive years. All participants had a blood sample taken for measurement of influenza antibody titers before receiving the influenza vaccine. Subsequently, the 2004-2005-A/New Caledonia/20/99(H1N1)-like, A/Wyoming/3/2003(H3N2), and B/Shanghai/361/2002-like antigens-and/or 2005-2006-A/New Caledonia/ 20/00(H1N1)-like, A/California/7/2004 (H3N2)-like, and B/Shanghai/361/2002-like antigens-influenza vaccine was administered intramuscularly. Serum was stored at -80°C until the day of analysis. A second blood sample was obtained 2 to 4 weeks later to measure antibody response.

[This substudy that was originally registered to NCT00205270 and subsequently registered to its own NCT number for the purpose of clarity in linked results]