The concerning Brazilian variant of coronavirus does not appear to affect vaccines, Downing Street has said.

It comes after a top virologist suggested a separate strain from Brazil is already in the country.

The Prime Minister’s official spokesman said scientists at the Government’s Porton Down research facility are currently investigating the new concerning strain, which has been detected in travellers to Japan.

It has led to travellers from South America and Portugal being banned from entering the UK.

Meanwhile, new official figures show 3.12m people have received a Covid-19 vaccine in Great Britain.

The PM’s spokesman said: “As with some of the other variants we’ve seen, the Kent (UK) variant and the South Africa variant, evidence does suggest that it (the concerning Brazil variant) may be more transmissible.

“More research is required to confirm this and Porton Down will conduct that research but current evidence does not suggest that the strain causes any higher mortality rate or that it affects the vaccines or treatments.”

Downing Street said it had acted “as quickly as possible” to impose the ban on travellers from South America, with the concerning Brazilian strain possibly posing a “significant risk to the UK”.

The Prime Minister’s official spokesman said: “It’s obviously right that we continue to look at different variants and take action accordingly.

“As soon as we identified this variant, our teams were quickly working on this and, given that we know this could pose a significant risk to the UK, we acted as quickly as possible, which is why you’ve seen this travel ban from those countries enacted quickly.”

Earlier, Professor Wendy Barclay, G2P-UK lead and head of department of infectious disease and chairwoman in influenza virology at Imperial College London, was forced to clarify her comments after at first suggesting the concerning strain may be in the UK.

She later said: “The new Brazilian variant of concern, that was picked up in travellers going to Japan, has not been detected in the UK.

“Other variants that may have originated from Brazil have been previously found.”

The virologist added that both Brazilian variants have mutations that suggest “they might impact the way that some people’s antibodies can see the virus”.

She added: “It is really important that we carry out this work now, and carry it out carefully, and in several different laboratories, to really firm up those results because they have big implications.”

Her comments came after Transport Secretary Grant Shapps said he was “not aware” of any cases of the concerning Brazilian strain in the UK which had led him to impose the restrictions, which came into force at 4am on Friday.

Elsewhere, Government scientists put the latest reproductive number – the R rate – for the UK at 1.2 to 1.3, for data examined up to January 11.

The R rate refers to the number of people that an infected person will pass the virus on to, with an R rate above 1 meaning the epidemic is still growing.

The scientists said: “There are some initial indications that areas that have had higher prevalence levels and been under tougher restrictions for a longer period of time (East of England, London, and South East) are experiencing a slight decline in the numbers of people infected.

“Regions such as the North West and South West continue to see infections rise, which is likely to reflect the spread of the new (UK) variant in these areas.

“The latest figures show that we need to remain vigilant to keep this virus under control, to protect the NHS and save lives.

“We all need to play our part, and if everyone continues to follow the rules, we can expect to drive down the R number across the country.”

Meanwhile, Cambridge University researchers have said the R is below 1 in the East of England, London, the South East, West Midlands and Yorkshire and the Humber.

But they believe it is still above 1 in the South West, North West, North East and East Midlands, indicating case numbers are growing in those regions.

Earlier, Dr Mike Tildesley, an epidemiologist who advises the Government on its scientific pandemic influenza group, said the UK was late in imposing its travel ban to prevent the concerning Brazilian strain entering Britain.

“We always have this issue with travel bans, of course, that we’re always a little bit behind the curve,” he told BBC Breakfast.

“My understanding is that there haven’t really been any flights coming from Brazil for about the past week, so hopefully the immediate travel ban should really minimise the risk.”

Dr Tildesley said that although scientists “don’t believe there is anything to worry about” in terms of vaccine efficacy, the higher transmissibility could mean “people potentially might end up developing severe symptoms more rapidly which could cause more issues with our health service”.