Modeling geographic vaccination strategies for COVID-19 in Norway.

Vaccination was a key intervention in controlling the COVID-19 pandemic globally. In early 2021, Norway faced significant regional variations in COVID-19 incidence and prevalence, with large differences in population density, necessitating efficient vaccine allocation to reduce infections and severe outcomes. This study explored alternative vaccination strategies to minimize health outcomes (infections, hospitalizations, ICU admissions, deaths) by varying regions prioritized, extra doses prioritized, and implementation start time. Using two models (individual-based and meta-population), we simulated COVID-19 transmission during the primary vaccination period in Norway, covering the first 7 months of 2021. We investigated alternative strategies to allocate more vaccine doses to regions with a higher force of infection. We also examined the robustness of our results and highlighted potential structural differences between the two models. Our findings suggest that early vaccine prioritization could reduce COVID-19 related health outcomes by 8% to 20% compared to a baseline strategy without geographic prioritization. For minimizing infections, hospitalizations, or ICU admissions, the best strategy was to initially allocate all available vaccine doses to fewer high-risk municipalities, comprising approximately one-fourth of the population. For minimizing deaths, a moderate level of geographic prioritization, with approximately one-third of the population receiving doubled doses, gave the best outcomes by balancing the trade-off between vaccinating younger people in high-risk areas and older people in low-risk areas. The actual strategy implemented in Norway was a two-step moderate level aimed at maintaining the balance and ensuring ethical considerations and public trust. However, it did not offer significant advantages over the baseline strategy without geographic prioritization. Earlier implementation of geographic prioritization could have more effectively addressed the main wave of infections, substantially reducing the national burden of the pandemic.

Intussusception among Norwegian children: What to expect after introduction of rotavirus vaccination?

BACKGROUND: To reduce the risk of vaccine-associated intussusception, rotavirus vaccination in Norway was implemented under strict age limits (the first dose given by 12 weeks of age and the second dose by 16 weeks of age) in 2014. We estimated the incidence of intussusception in children <2 years old before vaccine introduction and the number of vaccine-associated cases under current and extended age limits for vaccine administration in Norway. METHODS: To estimate the baseline incidence, we validated all diagnoses in children <2 years old registered in the national hospital registry during the pre-vaccine period of 2008-2013. Using national vaccine coverage data and international estimates of intussusception risk after rotavirus vaccination, we calculated the numbers of expected vaccine-associated intussusception cases to compare with the estimated numbers of averted rotavirus cases. Uncertainty was accounted for by several scenario analyses using current and extended age limits for vaccine administration. RESULTS: The pre-vaccine incidence of intussusception was 26.7 (95% CI 23.1-30.6) cases/year per 100,000 children <2 years old and 37.1 (95% CI 31.2-43.8) cases/year per 100,000 children <1 year old. In the 2016 birth cohort (approx. 60,000) vaccinated under the current age limits, 1.3 (95% CI 0.7-2.0) vaccine-associated intussusception cases were expected to occur. If age limits were extended to 16 weeks for the first vaccine dose and 24 weeks for the second dose, leading to more children vaccinated at an older age, 2.2 (95% CI 1.2-3.5) excess cases would be expected in the same cohort. Simultaneously, an estimated 1768 rotavirus hospitalizations/year in children <5 years old would be averted under current age limits, with 98 additional rotavirus hospitalizations averted under extended age limits. CONCLUSIONS: Administering rotavirus vaccines beyond current age limits in Norway would lead to a marginal increase in the number of intussusception cases, which would be offset by the benefits of vaccination.