Fewer than two dozen areas of England are yet to record a single case of the new Delta off-shoot, official figures suggest.
One of the Government's largest Covid surveillance programmes found AY.4.2 was in 294 of 315 local authorities (93 per cent) up to October 9, the latest day statistics are available for.
But there were 21 areas — scattered in pockets across the North East and North West — that still have not recorded a single case of the subtype.
It comes amid fears AY.4.2 is helping to turbo-charge outbreaks in parts of the South West, where cases have reached record highs in the wake of a laboratory testing blunder.
The strain is now behind more than one in five infections in areas of Devon, Wiltshire and Somerset, which have some of the fastest growing infection rates in the country. It makes up more than 10 per cent of infections across England, having doubled in the space of three weeks.
Scientists have raised concerns over AY.4.2 after it advanced from London and the South East to the rest of the country within a matter of weeks.
But yesterday they sought to dampen fears, saying it has taken four months to spread and is only 10 to 15 per cent more transmissible than Delta. Data shows it has not triggered the same explosive change as when Alpha was replaced this year.
The above maps show the proportion of cases that were AY.4.2 in the fortnight to September 25 (left) and October 9 (right). The darker colours indicate that a higher proportion of infections were down to this sub-variant.
The above graph shows the proportion of cases down to different variants in England over time. It reveals AY.4.2 (yellow) is beginning to make up a higher proportion of cases. But Delta (light green) remains the dominant Covid strain. Alpha (purple) was dominant last winter, after it replaced the old virus (pink and dark green)
SWINDON: There are growing fears AY.4.2 may be triggering an outbreak in this local authority. Its Covid cases have risen by 242 per cent in a week
SOUTH SOMERSET: There are also concerns AY.4.2 could be triggering an outbreak in this local authority. It is making up an increasingly larger proportion of cases, and the authority has seen its infections double in a week
WILTSHIRE: AY.4.2 cases are also rising in this local authority. Its Covid cases more than doubled in the latest week, prompting fears it may have triggered an outbreak there
MID-DEVON: There are also fears AY.4.2 has triggered a surge in cases in Mid-Devon. The variant is making up a growing proportion of cases here, while overall infections surged 97 per cent in the latest week