UK scientists have been investigating whether rats could infect humans with coronavirus - and whether the disease could mutate in wild rodents before being passed to people.
Researchers say laboratory evidence indicates that while rats and mice appear unable to contract the most common forms of COVID, the N501Y spike protein mutation found in several concerning variants "has an increased affinity" for rodents.
A report issued by the government's Scientific Advisory Group for Emergencies (SAGE) also found the likelihood that a variant of concern (VOC) that has arisen in humans could infect a rodent and then spread among the animals is high.
But it concluded that the risks of coronavirus adapting in rodents to create a new, worrying strain was low - and that any adaptation to rodent hosts would make it less transmissible among humans.
The report said: "There is a plausible pathway for infection of rodents with new variants of concern from infected humans following contamination of an environment.
"Experimental evidence has shown SARS-CoV-2 with N501Y has increased affinity for lab rodents and there is nothing to suggest the same would not be true for wild rodents.
"While rodents are a possible animal reservoir, the likelihood currently of a VOC emerging as a result of adaptation in rodents is low, and certainly lower than in the human population, as it is expected that adaptation to rodent hosts would reduce the virus' ability to transmit to or between humans."
Minutes of the latest SAGE meeting show 70% of England's population are currently having their sewage monitored for COVID, with samples collected and tested four times a week and data used to identify outbreaks and inform local responses.
Scientists involved in the studies say the risk of viable virus persisting in sewage or household waste was "very low", while conceding that if a rodent was infected this could result in "sustained transmission" among the animals.
However, the report added that considerable doubt remained over the potential for rodents to become "reservoirs for future outbreaks".
"There are key uncertainties around whether the VOC would become established in a rodent population, or would the virus become adapted to the rodent host and would no longer be able to infect a human or establish a new outbreak," it said.
"Therefore there remain some important questions about whether these populations could act as reservoirs for future outbreaks but targeted surveillance in human populations at a higher risk of exposure would answer some of those questions in time."