Sjúkdómar sem fyrirbyggja má með bólusetningum hjá börnum, unglingum og ungu fólki á Íslandi – rótaveira, meningókokkar og inflúensa: Er þörf á umbótum?

Vaccines are among the most important medical discoveries ever made and are the cornerstone of public health interventions. Public health authorities must be attentive to the local epidemiology of infectious diseases and the benefits of changing the immunisation schedule and introducing new vaccines into the national immunisation programmes. The aims of the thesis were to assess whether changes and improvements are needed to the Icelandic national immunisation programme regarding immunisations against rotavirus, Neisseria meningitidis and influenza. The thesis is comprised of four studies. In study I, the disease burden of rotavirus in young children in Iceland was assessed, as well as the cost-effectiveness of including rotavirus vaccinations in the national immunisation programme in Iceland. A two-year prospective study was conducted. Children under the age of six attending a paediatric emergency department with acute gastroenteritis were recruited. Stool samples were collected from participants, as well as information about the total duration of symptoms, the need for treatment in the emergency department and for hospital admissions, the number of days parents missed from work etc. Parents were also asked about their opinion on rotavirus vaccinations. Study I showed that rotavirus is the most common virus causing acute gastroenteritis leading to emergency department visits in young children in Iceland. Rotavirus causes a significant disease burden on young children, their parents, and the health care system. A substantial loss of productivity is attributable to rotavirus acute gastroenteritis, leading to considerable societal costs. The addition of a rotavirus vaccine to the national immunisation programme would be cost-effective and most parents are in favour of it. We conclude that rotavirus vaccines should be added to the national immunisation programme. Study II assessed the prevalence of asymptomatic meningococcal carriage in children, adolescents and young adults in Iceland, the prevalence of meningococcal capsular groups in colonisation and the duration of colonisation. Nasopharyngeal swabs were collected from 1–6-year-old children in daycare centres and oropharyngeal swabs from 15–16-year-old adolescents and 18–20-year-old young adults in the spring of 2019. Of 460 children, none carried meningococci. The colonisation prevalence was 0.5% among adolescents (1/197) and 6.5% among young adults (34/525). Non-groupable meningococci were most common in colonisation (26/35 carriers), followed by MenB (6/35 carriers). Two participants carried MenY and one carried MenW. No carriage of MenC, the group that is currently vaccinated against in Iceland, was detected. The longest duration of carriage was 21 months (from the first positive swab to the last positive swab). Meningococcal isolates from successive swabs from the same carrier were closely related, indicating a prolonged carriage with the same strain. Study II shows that meningococcal colonisation prevalence, especially of capsulated meningococci, is low in Iceland. Considering both the low colonisation prevalence and low incidence of invasive meningococcal disease, we conclude that changes in meningococcal vaccination strategies in the national immunisation programme are not currently needed. In study III, the humoral and cellular immune responses to influenza vaccinations were assessed in adolescents with obesity compared to adolescents with normal weight. Thirty adolescents with obesity and thirty adolescents with normal weight were recruited. The participants were vaccinated with a tetravalent influenza vaccine. Venous blood samples were collected before vaccination and again four weeks after vaccination. The results of study III show that both humoral and cellular immune responses to influenza vaccination are similar in adolescents with obesity and adolescents with normal weight. Therefore, changes are not needed to influenza vaccination methods for adolescents with obesity. Study IV assessed the influenza vaccine uptake in pregnant women in the ten influenza seasons 2010-2020, and the burden of influenza on pregnant women and their infants. The influenza vaccine uptake ranged from 6.2% in 2011-2012 to 37.5% in 2019-2020. Vaccinations against influenza in pregnancy protect pregnant women and their infants in the season of vaccination and provide probable protection for infants