Rotavirus Vaccine Safety and Effectiveness in Infants With High-Risk Medical Conditions.

OBJECTIVES: Rotavirus vaccination has 87% to 100% effectiveness against severe rotavirus acute gastroenteritis (AGE) in healthy infants in high-income countries. Little is known whether infants with medical risk conditions (MRCs) are equally protected and if the vaccine is equally well tolerated. We conducted a quasi-experimental prospective multicenter before-after cohort study to assess the vaccine effectiveness (VE) and safety profile of the human rotavirus vaccine (HRV) among MRC infants that required prolonged or frequent postnatal care. METHODS: The Netherlands has no national rotavirus immunization program, but HRV was implemented in routine care for MRC infants in 13 Dutch hospitals. Participants in the before and after cohort, HRV unvaccinated and vaccinated, respectively, were followed for occurrence of (rotavirus) AGE. VE of at least 1 dose was estimated by using time-to-event analysis for severe rotavirus AGE. Vaccine-related serious adverse event (AEs) after HRV were retrieved systematically from medical charts. Solicited AEs after vaccinations were prospectively collected and compared between vaccination time points with or without HRV. RESULTS: In total, 1482 high-risk infants with MRC were enrolled, including 631 in the before and 851 in the after cohorts; 1302 infants were premature (88.3%), 447 were small for gestational age (30.2%), and 251 had at least 1 congenital disorder (17.0%). VE against severe rotavirus AGE was 30% (95% confidence interval [CI]: -36% to 65%). Overall, the observed number of rotavirus hospitalizations was low and not significantly different between the cohorts (2 and 2, respectively). The rate of vaccine-related serious AE was 0.24 per 100 vaccine doses. The adjusted risk ratio for any AE after HRV vaccination compared with other routine vaccinations was 1.09 (95% CI: 1.05 to 1.12) for concomitant administration and 0.91 (95% CI: 0.81 to 0.99) for single HRV administration. Gastrointestinal AEs were 10% more frequent after HRV. CONCLUSIONS: In contrast to previous findings among healthy term infants, in routine use, HRV offered limited protection to vulnerable medical risk infants. HRV is generally well tolerated in this group in single administration, but when coadministered with routine vaccines, it is associated with higher risk of (mostly gastrointestinal) AE. Our study highlights the importance of studying vaccine performance in subgroups of medically vulnerable infants.

Evaluation of non-specific effects of human rotavirus vaccination in medical risk infants.

BACKGROUND: The WHO recommends research into non-specific effects of vaccination. For rotavirus vaccines, these have not yet been well established. We studied non-specific effects up to 18 months of age using data from a quasi-experimental before-after study comparing cohorts of rotavirus vaccinated and unvaccinated infants with medical risk conditions. METHODS: Infants were enrolled at six weeks of age before and after a stepped-wedge implementation of a hospital-based risk-group rotavirus vaccination program. Other infant vaccinations were administered according to the Dutch National Immunization Program and similar in both cohorts. Non-specific effect outcomes were prospectively collected using monthly questionnaires and included acute hospitalization (excluding for acute gastroenteritis), monthly incidence of acute respiratory illness and eczema. We used time-to-event analysis and negative binomial regression to assess the effect of at least one dose of rotavirus vaccination for each of these outcomes. Findings The analysis included 496 rotavirus unvaccinated and 719 vaccinated medical risk infants. In total, 1067 (88%) were premature, 373 (31%) small for gestational age and 201 (17%) had a congenital pathology. The adjusted hazard ratio for first acute hospitalization was 0·91 (95 %CI 0·76;1·16) for rotavirus vaccinated versus unvaccinated infants. Adjusted incidence rate ratio for acute respiratory illness was 1·05 (95 %CI 0·96;1·15) and for eczema 0·89 (95 %CI 0·69;1·15). CONCLUSION: The results suggest no, or minimal non-specific effects from rotavirus vaccination on acute hospitalization, acute respiratory illness or eczema in medical risk infants. TRIAL REGISTRATION: as NTR5361 in the Dutch trial registry, www.trialregister.nl.

Acute Gastroenteritis Disease Burden in Infants With Medical Risk Conditions in the Netherlands.

BACKGROUND: Infants with medical risk conditions are vulnerable to childhood infections including acute gastroenteritis (AGE). To guide prevention programs, we quantified AGE incidence, severity and virus prevalence among medical risk infants in the Netherlands. METHODS: This prospective cohort-study was part of the RIVAR-project recruiting infants with prematurity, low birth weight or severe congenital conditions in 13 hospitals. Follow-up included 18 monthly health questionnaires detailing AGE symptoms and healthcare usage. Parents were also instructed to notify when an infant developed AGE, to collect a stool sample and complete a daily severity score (Modified Vesikari Severity). Stool samples were analyzed by real-time polymerase chain reaction for rotavirus, norovirus, adenovirus and astrovirus. RESULTS: Between November 2014 and October 2017, 631 infants participated during 9125 person-months of observation. In total, 559 episodes were identified. The mean AGE incidence rate was 73.5 per 100 person-years (PY) (95% confidence interval: 67.6-79.9) and increased with age [incidence rate: 48.3 (39.8-58.3) vs. 80.2 (73.0-88.1)/100 PY for ages 1-5 vs. 6-18 months, respectively]. Healthcare was attended for 38.1% (213/559) and 26.8% (68/254) were classified as severe based on the Modified Vesikari Severity. Stool samples were obtained from 254 AGE episodes. Norovirus was identified in 65 (25.6%) and rotavirus in 44 (17.7%). Adenovirus and astrovirus together accounted for 8.3% (N = 21). Severe AGE occurred most frequently in rotavirus positive episodes. CONCLUSION: The observed AGE incidence, severity and healthcare usage among medical risk infants confirms substantial disease burden. Norovirus and rotavirus are the dominant pathogens and severe episodes occurred most frequently in children with rotavirus infection. AGE prevention in medical risk infants should be prioritized.

Association of Routine Infant Vaccinations With Antibody Levels Among Preterm Infants.

Importance: The standard schedule of national immunization programs for infants may not be sufficient to protect extremely and very preterm infants. Objective: To evaluate the immunogenicity of routine vaccinations administered to preterm infants. Design, Setting, and Participants: A multicenter, prospective, observational cohort study of preterm infants stratified according to gestational age recruited from 8 hospitals across the Netherlands between October 2015 and October 2017, with follow-up until 12 months of age (October 2018). In total, 296 premature infants were enrolled and compared with a control group of 66 healthy term infants from a 2011 study, immunized according to the same schedule with the same vaccines. Exposures: Three primary doses of the diphtheria-tetanus toxoids-acellular pertussis-inactivated poliomyelitis-Haemophilus influenza type b-hepatitis B combination vaccine were given at 2, 3, and 4 months after birth followed by a booster at 11 months and a 10-valent pneumococcal conjugate vaccine at 2, 4, and 11 months after birth. Main Outcomes and Measures: Primary end points were (1) proportion of preterm infants who achieved IgG antibody against vaccine antigens at concentrations above the internationally defined threshold for protection after the primary series and booster dose and (2) serum IgG geometric mean concentrations after the primary series and booster vaccination. Proportions and geometric mean concentrations were compared in preterm infants and the control group of term infants. Results: Of 296 preterm infants (56.1% male; mean gestational age, 30 weeks), complete samples before vaccination, 1 month after the primary series, and 1 month after the booster were obtained from 220 preterm infants (74.3%). After the primary series, the proportion of preterm infants across all gestational age groups who achieved protective IgG antibody levels against pertussis toxin, diphtheria, tetanus and 6 of 10 pneumococcal serotypes varied between 83.0% and 100%, Haemophilus influenzae type b between 34.7% and 46.2% (40.6% among all preterm infants overall), and pneumococcal serotypes 4, 6B, 18C, and 23F between 45.8% and 75.1%. After the booster dose, protective antibody levels were achieved in more than 95% of all preterm groups, except for Haemophilus influenzae type b (88.1%). In general, geometric mean concentrations of all vaccine-induced antibodies were significantly lower in all preterm infants vs term infants, except for pertussis toxin and pneumococcal serotypes 4 and 19F after the primary series and booster vaccination. Conclusions and Relevance: Among preterm infants, administration of routine vaccinations during the first year of life was associated with protective antibody levels against most antigens in the majority of infants after the primary series and booster, except for Haemophilus influenzae type b. However, antibody concentrations were generally lower among preterm infants compared with historical controls.

Timeliness of immunisations in preterm infants in the Netherlands.

BACKGROUND: In the Netherlands, preterm infants receive the immunisations at the same chronological age as recommended for term infants without correction for gestational age (GA). The aim of this paper was to describe the timeliness of the routine Dutch national immunisation schedule in preterm infants in their first year of life and to evaluate possible determinants of delay. METHODS: Preterm infants were prospectively recruited between October 2015 and October 2017 and stratified according to GA (<28, 28-32 and 32-36 weeks). Data from the baseline parental questionnaire, monthly parental questionnaires and medical records were used to determine the immunisation age and proportion of infants timely receiving the first immunisations (between 42 and 63 days). Results were compared between the GA and birth weight (BW) groups. Determinants associated with timeliness of immunisation were studied by multivariate logistic regression analysis. RESULTS: Timely start of immunisation occurs in 60.5% of preterm infants in the Netherlands. The proportion of infants receiving the first immunisation on time was lowest for the group with GA <28 weeks (37%). The mean age of the first immunisation across all GA groups was 62.7 days (range 33-118) and differed significantly between GA group <28 weeks and the other two GA groups of 28-32 and 32-36 weeks (p < 0.001). Similar results were seen when stratified by BW. Multivariate analysis showed that low socioeconomic status (SES) and prolonged hospitalisation beyond 37 weeks each negatively influenced timeliness of the first immunisation. CONCLUSION: These findings indicate that start of immunisations was often delayed in prematures and differs for different GA groups, being lowest (37%) in infants <28 weeks GA. Lower SES and prolonged hospital stay beyond 37 weeks GA are important determinants of timeliness. Efforts to improve timeliness should focus most on counselling parents in lower SES.