Conflict of interest: LS is a co-investigator in an unrelated study, for which THL has received research funding from GlaxoSmithKline Vaccines. The other authors report no potential conflicts of interest.
Authors’ contributions: All authors attest they meet the ICMJE criteria for authorship. All authors have contributed to, seen and approved the final version of the manuscript.
AH set up and performed MN tests, participated in laboratory confirmation of COVID-19 suspicions, coordinated and participated in the collections of the Finnish population sera, and wrote the manuscript.
TS performed the whole genome sequencing and genetic characterisation.
SK and JH performed the IFA and WB analysis, respectively.
PÖ isolated the virus and was responsible of the SARS-CoV-2 related biosafety level 3 laboratory work at THL.
MP, MS, TP and JS participated in THL COVID-19 situation monitoring group work of THL.
SB and MM participated in serological analysis planning group of THL. SB contributed in the interpretation of MN results.
ER set up the real-time RT-PCR method at THL and participated in laboratory confirmation of COVID-19 suspicions.
AK and TS participated in collection of the convalescent serum. AK had a significant role to organising convalescent serum sampling.
HKK, LM and ML were in charge of primary diagnostic of COVID-19 suspicions in HUSLAB. HKK and LM also set up the real-time RT-PCR method at HUSLAB and participated in laboratory sample logistics from HUSLAB to THL.
MB was responsible for the care of the patient in hospital.
MJ and LS participated in interviewing the index case and contact tracing.
OV was responsible for virological and serological studies in HUSLAB and University of Helsinki, participated in the designing of the study and organising convalescent serum sampling.
NI and CSK were responsible of THL laboratory confirmation of COVID-19 suspicions, participated in COVID-19 situation monitoring group work of THL and laboratory sample logistics. CSK was also responsible for the collections of the Finnish population sera and participated in the designing of the study.