The research, as it makes clear, has not yet been peer reviewed.These are the conclusions it makes.
“The key conclusions of our analysis are as follows:
The UK epidemic comprises a very large number of importations due to inbound international travel2. We detect 1356 independently-introduced transmission lineages, however, we expect this number to be an under-estimate.
The speed of detection of UK transmission lineages via genome sequencing has increased through time.
Many UK transmission lineages now appear to be very rare or extinct, as they have not been detected by genome sequencing for >4 weeks.
The rate and source of introduction of SARS-CoV-2 lineages into the UK changed substantially and rapidly through time. The rate peaked in mid-March and most introductions occurred during March 2020.
We estimate that ≈34% of detected UK transmission lineages arrived via inbound travel from Spain, ≈29% from France, ≈14% from Italy, and ≈23% from other countries [100%]. The relative contributions of these locations were highly dynamic.
The increasing rates and shifting source locations of SARS-CoV-2 importation were not fully captured by early contact tracing.
Our results are preliminary and further analyses of these data are ongoing.”