PHE experts are urgently carrying out an analysis of the new variant.
They said there is no evidence to suggest the strain makes vaccines less effective.
Most of the cases have been linked to overseas travel and there is currently no evidence of community transmission in the UK, PHE added.
PHE is performing laboratory tests to better understand the impact of mutations on the behavior of the virus.
PHE also released data today showing that cases of the Delta variant have increased by 33,716 since last week to a total of 286,765.
The variant now accounts for 99% of all cases in the UK.
Other data released today shows that between June 21 and July 19, 1,788 people were admitted to hospital after testing positive for the Delta variant.
Of these, 54.3 percent were unvaccinated and 29.6 percent had received both doses of the vaccine.
Public Health England said in a statement: “Sixteen confirmed cases of B.1.621 have been identified across the country to date, and the majority have been linked to overseas travel.
“There is currently no evidence of community transmission in the UK.
“There is currently no evidence that this variant causes more severe disease or makes currently deployed vaccines less effective.
“PHE is performing laboratory tests to better understand the impact of mutations on the behavior of the virus. “
It comes as the percentage of people testing positive for Covid-19 is believed to have increased in all parts of England except the North East and North West, where the trend is “uncertain”, said the ONS.
The north-east of England had the highest proportion of people of any region likely to test positive for the coronavirus in the week to July 17 – around one in 45 people.
North West England had the second highest estimate at around one in 55.
The east of England had the lowest estimate at around one in 110.
PHE still insisted today that the British continue to be vaccinated.
Dr Jenny Harries, Managing Director of the UK Health Security Agency, said: “These most recent hospitalization data shows once again how crucial vaccination is in protecting us from serious illness and death.
“Two doses of the vaccine is much more effective against COVID-19 than a single dose, so be sure to show up for your second dose as soon as you are prompted.
“As we move out of restrictions and immunization coverage continues to increase, it is important to remember that while the protection offered by immunization is great, it is not complete. It is still as important as ever that we continue to exercise caution. “