New York City is experiencing rapid growth of Covid-19 variants, Mayor Bill de Blasio and health officials said on Wednesday, showing the importance of a swift vaccine distribution campaign.
The UK variant and a new locally identified strain are spreading rapidly in the city and account for 51 per cent of Covid-19 cases.
A new variant identified in Washington Heights in New York is being investigated after two research teams in New York and California revealed they had found variants in late February.
The strain, B1526, has spread quickly in the city, which recorded a seven-day average of 3,640 coronavirus cases.
It accounted for 39 per cent of positive samples in the past week, up from 31 per cent the previous week.
"Our preliminary analysis is that it is probably more infectious than older strains of the virus," said Dr Jay Varma, the city's senior public health adviser.
"It may be similar in infectiousness to the UK strain, and our preliminary analysis does not show that this new strain causes more severe illness or reduces the effectiveness of vaccines."
Dr Varma said the findings he disclosed on Wednesday were "preliminary".
The UK variant accounts for a large portion of the city's case growth. It is present in 12 per cent of cases, up from 8 per cent the previous week.
The strains identified in Brazil, South Africa and the UK, declared to be "variants of concern" by the World Health Organisation, are also spreading in the city.
A new study found the UK strain could be up to twice as deadly as other variants.
"So far, thank God, what we're finding is that variants are not posing the worst kind of problems we might fear," Mr de Blasio said Wednesday.
"For example, a variant that is more deadly, we're not seeing that. A variant that is vaccine-resistant, we're not seeing that.
"What we are seeing is variants that are more infectious and therefore spread the disease more, and that's a real issue.
"But the good news is we have the strategies to fight back."
The city is advancing in its vaccination programme, which involves mass centres at high-capacity, high-profile sites including the Javits Centre and Yankee Stadium, some of which are operating around the clock.
About 35 per cent of the city's adult population has received at least one dose of vaccine, while 18 per cent of adults have been fully vaccinated, the Department of Health says.
All three approved vaccines in the US, including the newly approved, single-dose Johnson & Johnson vaccine, are being distributed throughout the city.
New York City became the global centre for the pandemic last year in late March and early April, overwhelming hospitals and triggering an intense lockdown.
The city marked a year since its first coronavirus case on March 2.