Little evidence suggests Cambridge University students transmitted coronavirus to members of the local public in October and November last year, a recent study has concluded.
The study follows a partnership between the COVID-19 Genomics UK Consortium (COG-UK) and the University of Cambridge, which offered regular SARS-CoV-2 tests to all students living in its colleges, even if they show no symptoms, and to symptomatic students and staff.
Around 12,000 students (80% of those eligible) signed up to the asymptomatic screening programme. Test results from the first five weeks of the autumn term helped scientists track how infections spread within the student population.
Using data from COG-UK, the Cambridge scientists identified little evidence of cross-transmission between Cambridge students and those living in the city, because the different clusters of infections came from different strands of the Covid-19 genetic family.
The study concluded that 90% of infections at Cambridge University related to three lineages of Covid-19, and that the outbreaks likely related to “a small number of transmission events early on”. It also concluded that most of the different clusters do not appear to have spread between colleges; this evidence suggests that infection control measures helped contain the spread.
In half of the cases relating to one of the largest clusters of infections, patients were asymptomatic.
By comparing the genetic code of positive Covid samples, scientists can plot a genetic ‘family tree’ to determine whether two cases are related. As a virus spread, it acquires mutations – meaning scientists can plot where clusters of infections stemmed from.
Asymptomatic screening can help identify cases of infection early, including where students are unaware of the infection, and inform infection control measures. This has never been more urgent, with the emergence of the new variant
– Prof Patrick Maxwell, University of Cambridge
The largest cluster included 139 cases by week five and was the source of ongoing transmission within the university. It included students from a number of colleges, courses and years of study. The university said it is not clear whether these can be traced back to a single event that led to its dispersal across the university.
Dr Dinesh Aggarwal from the department of medicine at the University of Cambridge and a member of COG-UK said: “It appears that a few instances of the virus being introduced to the university account for the majority of cases of established transmission. This suggests to us that in most cases when a virus was introduced, students behaving responsibly and complying with infection control measures helped stop the virus in its tracks.
“We hope it will be particularly reassuring that so far we have not found evidence of substantial transmission between our students and the local community.”
Dr Ben Warne, a clinical research fellow and one of the leads on the university’s asymptomatic screening programme, added: “It’s clear we need to better understand how the virus spreads between students on different courses and at different colleges. Once established, these widely-distributed outbreaks are more challenging to control, potentially resulting in the continued spread. Genomics should help us piece together this puzzle and help us target prevention strategies.”
Prof Patrick Maxwell, Regius professor of physics at the University of Cambridge, said: “Getting our screening programme up and running in time for the start of term was no small order, but we believe it has paid off. Asymptomatic screening can help identify cases of infection early, including where students are unaware of the infection, and inform infection control measures. This has never been more urgent, with the emergence of the new variant.”