By Dr. Mallika Marshall

BOSTON (CBS) — A highly contagious variant of the coronavirus first identified in the U.K. has been spreading quickly throughout that nation. A new study suggests that college students returning home for Christmas could have caused more than 9,000 secondary infections.

How did they arrive at that number?

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Dr. Mallika Marshall: A new model devised by mathematicians at Cardiff University in Wales estimates that a student infected with coronavirus returning home from university for the holidays, would, on average, have infected just less than one other household member. So, if a million students returned home and if only 1% of them were infected, that could lead to 9,400 new household cases across the country. That doesn’t even take into account additional transmission if students took public transportation or engaged with friends or family outside of their household.

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We know that this fast-spreading variant has now been detected in a Massachusetts woman who traveled to the U.K. What can colleges and universities do to limit the spread by students returning home from school?

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Dr. Mallika Marshall: This new variant has now been detected in dozens of patients in various states around the U.S., including now in Massachusetts. Universities can discourage students from socializing in the days before leaving campus and provide mass testing of students before they return home. Families can wear masks in the home and limit contact with their student until he or she passes a quarantine period, for example, seven days with a negative test or 14 days without testing. Students should also be discouraged from seeing friends or other family members indoors or without masks.

Dr. Mallika Marshall