Dr Jay Varma, Bill de Blasio’s Covid tsar during the height of the pandemic, said the stubbornly high number of reported positive cases indicated that another spike was likely.
“The decline of reported COVID 19 cases in NYC has stopped. Reported cases are at a high plateau, which means actual transmission is very high... This is likely the beginning of a BA.5 wave,” Dr Varma tweeted.
The BA.5 variant was first detected in South Africa in December and is considered by experts to be the most dangerous strain yet for its ability to sidestep antibodies from past infections or vaccination and overcome immunity.
Transmission of Covid cases in New York have been on the increase since hitting two-month lows last week.
Dr Varma, an epidemiologist at Weill Cornell, said the fact that infections rates had remained high and stable in New York indicated another wave was likely to occur.
“Experience from other countries means there will be another big increase in NYC COVID 19 infections, including among those who have had Omicron in past few months.”
According to New York Health Department testing, BA.5 cases now account for 33 per cent of infections.
Nationwide, the BA.5 variant makes up 37 per cent of new cases, according to figures from the CDC.
Hospitalisations and death rates continue to fall, and Dr Varma said it was unclear what impact the rise in BA.5 cases would have on those numbers.
“At a minimum, can be confident predicting that BA.5 will lead to more days when people are out of work, kids home from school/camp, & more people suffering from Long COVID.”
On Thursday, the Food and Drug Administration told vaccine makers that any booster shots tweaked for the fall will have to add protection against the newest omicron relatives.
They recommended combination shots that add protection against the BA.4 and BA.5 omicron variants.