Objective: To determine if children born preterm were at increased risk of influenza hospitalization up to age five. Methods: National registry data on all children born in Norway between 2008 and 2011 was used in Cox regression models to estimate adjusted hazard ratios (aHR) for influenza hospitalizations up to age five in children born preterm (<37 pregnancy weeks). HRs were also estimated separately for very preterm (<32 weeks), early term (37-38 weeks), and post-term (≥42 weeks) children. Results: Among 238 628 children born in Norway from January 2008 to December 2011, 15 086 (6.3%) were born preterm. There were 754 (0.3%) children hospitalized with influenza before age five. The rate of hospitalizations in children born preterm was 1.4 per 10 000 person-years (95% confidence interval [CI]: 1.1-1.7), and 0.6 per 10 000 person-years (95% CI: 0.5-0.6) in children born at term (≥37 weeks). Children born preterm had a higher risk of influenza hospitalization before age 5: aHR 2.33 (95% CI: 1.85-2.93). The risk increased with decreasing gestational age and was highest among those born very preterm; aHR 4.07 (95% CI: 2.63-6.31). Compared to children born at 40-41 weeks, children born early term also had an elevated risk of influenza hospitalization; aHR (37 weeks) 1.89 (95% CI: 1.43-2.40), aHR (38 weeks) 1.43 (95% CI: 1.15-1.78). Conclusion: Children born preterm had a higher risk of influenza hospitalizations before age five. An elevated risk was also present among children born at an early term. Children born preterm would benefit from influenza vaccinations.

Background Accurate estimates of SARS-CoV-2 infection in different population groups are important for the health authorities. In Norway, public infection control measures have successfully curbed the pandemic. Military training and service are incompatible with these measures, and therefore stricter infection control measures were necessary in the Norwegian Armed Forces. We present the measures, and discuss the results and their value. We report on the seroprevalence of SARS-CoV-2 and the changes in antibody levels over six weeks. Methods In April 2020, 1170 healthy conscripts (median age 20 years) were enrolled. The infection control measures included a pre-enrollment telephone interview and self-imposed quarantine. Questionnaire data and serial SARS-CoV-2 PCR and serology testing were used to estimate the incidence of confirmed SARS-CoV-2, describe symptoms and monitor titer levels over a six week period. Results The seroprevalence of SARS-CoV-2 was 0. 6 %. Only 0. 2 % had a positive PCR for SARS-CoV-2 at the enrollment day. Serological titer levels increased up to nearly five-fold over the observation period. Eighteen conscripts reported mild respiratory symptoms during the 14 days prior to enrollment (all were PCR negative, one had positive serology), whereas 17 conscripts reported respiratory symptoms and nine had fever at the day of enrollment (all were PCR and serology negative). Conclusions The prevalence of SARS-CoV-2 in young adults in Norway is less than 1%. Testing of asymptomatic conscripts seems of no value in times of low COVID-19 prevalence. SARS-CoV-2 antibody titer levels increased substantially over time in youths with mild symptoms.