No evidence for added value of introducing mandatory COVID-19 testing for international travellers entering Norway with a valid EU digital COVID certificate

Background As a response to the emergence of the new Omicron SARS-CoV-2 variant, on December 3, 2021, mandatory testing after entry to Norway was extended to include international travellers with a valid COVID-19 certificate. We aim to validate if mandatory testing upon arrival increased the proportion of travellers confirmed with a positive COVID-19 test after entry. Methods We used individual level data on registered travellers linked with data on COVID-19 testing and confirmed COVID-19 cases. The proportions of confirmed cases among international travellers before and after the requirement were introduced was analysed with an interrupted times series design. Results The proportion of travellers with an EU COVID-19 certificate tested at an official test station increased from 3% to 43% after mandatory testing was introduced. However, the proportion of all travellers confirmed with COVID-19 rose only marginally with 0.14 percentage point directly after the intervention (p-value .06). The results are limited by the absence of data on antigen tests taken by the traveller at home and missing data from travellers without a valid Norwegian ID. Conclusions Our findings suggest that the benefit of mandatory testing of all international travellers to Norway was marginal in the period directly after the emergence of the omicron variant. This result must be understood in the context of free of charge testing at official test centres, a government recommendation on a low threshold to test when experiencing symptoms in addition to limited surveillance of the compliance of the test after arrival requirement.