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Publication

Vaccination in individuals/patients and populations at risk

Book - Dissertation

Vaccination does not only provide direct protection against infectious diseases but also contributes to the protection of an entire population when a large proportion of the population is vaccinated and herd immunity is reached. This way vulnerable individuals, namely those who cannot be vaccinated and those who do not respond to vaccination, can also be protected.My PhD project includes different projects which are related to the direct and indirect protection of patients and individuals at risk.In a first project, we have performed a phase III clinical trial on the safety and immunogenicity of a ninevalent vaccine against Human Papillomavirus (HPV) (Gardasil-9®) in 171 solid-organ transplant (SOT) patients and 100 HIV patients. As chronic HPV-infection is more prevailing among these patients, they have an increased risk of developing genital warts and (pre)cancerous lesions of the uterus, vagina, anus or penis. Whereas in healthy persons, HPV vaccination has proven to be very efficacious in preventing HPV infections, little is known for these patients. We found that all HIV patients seroconverted for all HPV types included in the vaccine (HPV 6/11/16/18/31/33/45/52/58), but seroconversion ranged from 46% for HPV45 to 72% for HPV58 among SOT patients. Seroconversion rates were particularly low in lung transplant patients for HPV18 (38%), HPV31 (43%) and HPV45 (32%). The vaccine was found to be safe and well tolerated in both patient groups.In a second project we assessed whether the current vaccination programs provide adequate protection to at-risk patients. Therefore, in different groups of at-risk patients we evaluated their vaccination status and degree of protection to some vaccine-preventable diseases. We found that many at-risk patients were inadequately vaccinated. In particular, only 44% of adult subjects were vaccinated against influenza, 32% against pneumococcal disease, 29% against diphtheria-tetanus and 10% against pertussis. Moreover, except for tetanus, the vast majority of at-risk patients remains susceptible to vaccine-preventable diseases such as diphtheria and pertussis. We found that seroprotective titers were reached in 83% of adult at-risk patients for tetanus (≥0,1IU/ml), 29% for diphtheria (≥0,1IU/ml), and seropositive titers in 22% for pertussis (≥5IU/ml). In pediatric patients, the seroprevalence of antibodies was 83.3% for measles (≥150mIU/ml), 82.9% for mumps (≥230 labU/ml) and 80.6% of children was protected against rubella (≥10IU/ml). Most pediatric patients were protected against tetanus (≥0.1IU/ml; 93.2%), but only 61.3% were protected against diphtheria (≥0.1IU/ml) and 53.2% had antibodies (≥5 IU/ml) against pertussis. Based on these results, we advocate for a closer follow-up of vaccination status.In a third project we aimed to increase influenza vaccination coverage in healthcare workers and as such to avoid transmission of influenza to vulnerable patients. A practical manual was developed for the organization of seasonal influenza vaccination campaigns (http://www.laatjevaccineren.be/hou-griep-uit-je-team). The use of the manual was evaluated in 11 nursing homes and was associated with a 10 to 30% increased vaccination uptake.