A new study from the university of Oxford has shed new light on how variants of the SARS-CoV-2 virus, which causes Covid-19, manage to spread despite measures taken to combat them.
The study, the largest of its kind, looked at the alpha variant of the virus, previously known as the Kent or British variant. At one time it was thought that the variant was 80% more transmissible than the standard virus, which accounted for its rapid spread.
But the new study shows that is not true. In fact, the alpha variant spread by a succession of ‘super-seeder’ events.
The variant was first identified in a major outbreak in Kent and Greater London, and from there it spread to other parts of England, Wales, Scotland and Northern Ireland. And the success of its spread is due to the fact that it had already colonised other territories long before the scientific community followed by the political powers had time to make any moves against it.
“As people travelled from London and the South East to other areas of the UK they ‘seeded’ new transmission chains of the variant,” explained lead author of the study, Dr. Moritz Kraemer of the department of zoology at Oxford.
“This continued as a national ‘super-seeding’ event which did not start to slow until early January. Although travel restrictions were introduced on 20 December, the exponential growth in Alpha variant cases compensated for this.”
In short, by the time travel restrictions were introduced, the variant had exported itself, and no restrictions could make any difference.
The study should be useful in demonstrating how scientists need to work more closely together to accurately estimate the transmissibility of variants, so that such super-seeder events can be avoided.
Unfortunately, it comes too late to do anything about the delta variant currently on the loose in the UK, while the government has lifted virtually all restrictions in England.
“As new variants emerge, we expect they will spread significantly before travel restrictions are put in place, as likely happened with the Delta variant,” Dr Kraemer said. “Given the scale of its current outbreak, it seems probably that the UK is now an important exporter of the Delta variant across Europe and some other parts of the world.”
But if that’s the case, why have the restrictions been lifted?
“The UK has decided to ease its restrictions because of our high vaccination rates and a confidence that we have protected the most vulnerable people in society. But that is not the case in most other countries, and the Delta variant could be starting this process again elsewhere, highlighting the urgent need for faster and equitable distribution of vaccines worldwide.”
The study is published in the current issue of the journal Science.
