University of Cambridge press release
Analysis finds little evidence of substantial transmission of virus between students and local community in first five weeks of term.
Since the start of the academic year in October 2020, the University of Cambridge has been offering regular SARS-CoV-2 tests to all students living in its Colleges, even if they show no symptoms. Initial results suggest that the screening programme, together with the University’s public health measures and responsible student behaviour, has helped limit the spread of the virus.
Now, the team running the programme has joined up with researchers at the COVID-19 Genomics UK Consortium (COG-UK) to track how infections spread among the student population. They have shown how a small number of transmission events early on were likely responsible for most of the infections at the University and found little evidence of substantial transmission of SARS-CoV-2 between students and the local Cambridge community in the first five weeks of term.
Around 12,000 students living in College accommodation (80% of eligible students) signed up to the asymptomatic screening programme, which uses a pooled sample approach to reduce the number of tests to fewer than 2,000 per week. In the first weeks of term, 1-2 students from each ‘household’ were tested each week; this has now increased to all participating students being tested each week. In addition, the University offers tests to students and staff who show symptoms of potential COVID-19.
The University is also playing a leading role in COG-UK, which is sequencing the genetic code of samples of the virus isolated from infected individuals to help better understand the spread of infection. As a virus spreads, its genetic code acquires mutations. By comparing the genetic code of samples, it is possible to plot a genetic ‘family tree’ known as phylogenetic tree and to say, coupled with epidemiological information, whether two cases are related – identical or almost-identical samples are likely to be closely related, while genomes with a larger number of genetic differences are less likely to be related.
As part of this work, COG-UK is analysing virus samples from students identified as positive through the University of Cambridge’s testing programmes and comparing them to samples taken from people in the wider Cambridge community. COG-UK and the University have released their interim report, covering the first five weeks of term.
The analysis showed that in week two, 90% of infections were confined to three lineages (related viral genomes). This lack of diversity suggests that a small number of transmission events at the start of term led to the majority of infections in the University.
Outbreaks that have largely been restricted to single Colleges appear to have been contained, suggesting that measures to prevent spread of the virus were successful. In one of the largest clusters (which included 32 cases by week three), half of the students were asymptomatic, highlighting the importance of screening programmes in helping identify infected individuals.
The largest cluster of cases (139 cases by week five, including 135 students, 1 staff member and 3 individuals from the local community) was the source of ongoing transmission within the University. It included students from a number of Colleges, courses and years of study. However, it is not clear whether these can be traced back to a single event that led to dispersion amongst colleges and courses.