tetano
Editor, Senior Moderator
Euro Surveill
. 2024 Oct;29(41).
doi: 10.2807/1560-7917.ES.2024.29.41.2400021. Early unrecognised SARS-CoV-2 introductions shaped the first pandemic wave, Sweden, 2020
Robert Dyrdak[SUP] 1 2 [/SUP], Emma B Hodcroft[SUP] 3 4 [/SUP], Sandra Broddesson[SUP] 1 [/SUP], Malin Grabbe[SUP] 1 2 [/SUP], Hildur Franklin[SUP] 5 [/SUP], Magnus Gisslén[SUP] 6 7 8 [/SUP], Maricris E Holm[SUP] 9 [/SUP], Magnus Lindh[SUP] 9 8 [/SUP], Joanna Nederby-Öhd[SUP] 10 11 [/SUP], Johan Ringlander[SUP] 9 8 [/SUP], Martin Sundqvist[SUP] 12 5 [/SUP], Richard A Neher[SUP] 13 3 [/SUP], Jan Albert[SUP] 1 2 [/SUP]
Affiliations
BackgroundDespite the unprecedented measures implemented globally in early 2020 to prevent the spread of SARS-CoV-2, Sweden, as many other countries, experienced a severe first wave during the COVID-19 pandemic.AimWe investigated the introduction and spread of SARS-CoV-2 into Sweden.MethodsWe analysed stored respiratory specimens (n = 1,979), sampled 7 February-2 April 2020, by PCR for SARS-CoV-2 and sequenced PCR-positive specimens. Sequences generated from newly detected cases and stored positive specimens February-June 2020 (n = 954) were combined with sequences (Sweden: n = 730; other countries: n = 129,913) retrieved from other sources for Nextstrain clade assignment and phylogenetic analyses.ResultsTwelve previously unrecognised SARS-CoV-2 cases were identified: the earliest was sampled on 3 March, 1 week before recognised community transmission. We showed an early influx of clades 20A and 20B from Italy (201/328, 61% of cases exposed abroad) and clades 19A and 20C from Austria (61/328, 19%). Clade 20C dominated the first wave (20C: 908/1,684, 54%; 20B: 438/1,684, 26%; 20A: 263/1,684, 16%), and 800 of 1,684 (48%) Swedish sequences formed a country-specific 20C cluster defined by a spike mutation (G24368T). At the regional level, the proportion of clade 20C sequences correlated with an earlier weighted mean date of COVID-19 deaths.ConclusionCommunity transmission in Sweden started when mitigation efforts still focused on preventing influx. This created a transmission advantage for clade 20C, likely introduced from ongoing cryptic spread in Austria. Therefore, pandemic preparedness should have a comprehensive approach, including capacity for large-scale diagnostics to allow early detection of travel-related cases and community transmission.
Keywords: COVID-19 pandemic; SARS-CoV-2; epidemiology; phylogenetics; viral respiratory tract infection.
. 2024 Oct;29(41).
doi: 10.2807/1560-7917.ES.2024.29.41.2400021. Early unrecognised SARS-CoV-2 introductions shaped the first pandemic wave, Sweden, 2020
Robert Dyrdak[SUP] 1 2 [/SUP], Emma B Hodcroft[SUP] 3 4 [/SUP], Sandra Broddesson[SUP] 1 [/SUP], Malin Grabbe[SUP] 1 2 [/SUP], Hildur Franklin[SUP] 5 [/SUP], Magnus Gisslén[SUP] 6 7 8 [/SUP], Maricris E Holm[SUP] 9 [/SUP], Magnus Lindh[SUP] 9 8 [/SUP], Joanna Nederby-Öhd[SUP] 10 11 [/SUP], Johan Ringlander[SUP] 9 8 [/SUP], Martin Sundqvist[SUP] 12 5 [/SUP], Richard A Neher[SUP] 13 3 [/SUP], Jan Albert[SUP] 1 2 [/SUP]
Affiliations
- PMID: 39392000
- DOI: 10.2807/1560-7917.ES.2024.29.41.2400021
BackgroundDespite the unprecedented measures implemented globally in early 2020 to prevent the spread of SARS-CoV-2, Sweden, as many other countries, experienced a severe first wave during the COVID-19 pandemic.AimWe investigated the introduction and spread of SARS-CoV-2 into Sweden.MethodsWe analysed stored respiratory specimens (n = 1,979), sampled 7 February-2 April 2020, by PCR for SARS-CoV-2 and sequenced PCR-positive specimens. Sequences generated from newly detected cases and stored positive specimens February-June 2020 (n = 954) were combined with sequences (Sweden: n = 730; other countries: n = 129,913) retrieved from other sources for Nextstrain clade assignment and phylogenetic analyses.ResultsTwelve previously unrecognised SARS-CoV-2 cases were identified: the earliest was sampled on 3 March, 1 week before recognised community transmission. We showed an early influx of clades 20A and 20B from Italy (201/328, 61% of cases exposed abroad) and clades 19A and 20C from Austria (61/328, 19%). Clade 20C dominated the first wave (20C: 908/1,684, 54%; 20B: 438/1,684, 26%; 20A: 263/1,684, 16%), and 800 of 1,684 (48%) Swedish sequences formed a country-specific 20C cluster defined by a spike mutation (G24368T). At the regional level, the proportion of clade 20C sequences correlated with an earlier weighted mean date of COVID-19 deaths.ConclusionCommunity transmission in Sweden started when mitigation efforts still focused on preventing influx. This created a transmission advantage for clade 20C, likely introduced from ongoing cryptic spread in Austria. Therefore, pandemic preparedness should have a comprehensive approach, including capacity for large-scale diagnostics to allow early detection of travel-related cases and community transmission.
Keywords: COVID-19 pandemic; SARS-CoV-2; epidemiology; phylogenetics; viral respiratory tract infection.
