The highly transmissible delta variant is now the most dominant COVID-19 strain in New York City, soaring from about a quarter of tested positive samples to more than 40% in a week as the five boroughs’ rolling seven-day case average surged 62%, according to new health department data out Friday.

As of Friday, the delta variant that first devastated India before spreading globally — and is thought to be up to 60% more contagious than that first widely tracked alpha variant — accounts for 41% of citywide samples tested in the last four weeks.

That’s up from 26% in the city’s variant report a week ago and up from 4.9% in about six weeks, a rise reflective of a national trend that saw delta emerge as America’s most dominant COVID variant last week.

It took only 14 days for delta to vault from the fourth most common COVID strain in the city to the first, overtaking first the so-called New York City strain that initially emerged in Washington Heights before spreading elsewhere, B.1.526, then gamma, formerly known as the Brazilian strain, P.1 and now alpha.

Scientific evidence has shown delta spreads far more easily than earlier strains of the virus and causes more severe outcomes for those infected, prompting renewed pushes at all levels of government to get people vaccinated if they haven’t been.

Delta, the variant that was first found in India and is now in at least 104 countries, has dramatically increased its prevalence across the U.S. over the last month, accounting now for well more than 50% of tested samples, according to the CDC.

The World Health Organization, which has called it the “fastest and fittest” variant yet, expects it to become the dominant strain globally.

Given the relatively minute subset of positive samples sequenced to assess potential strain variations, both CDC and local experts believe the prevalence of delta, which is classified as a variant of concern, to be much higher than reported.

The Delta variant of COVID-19 is in New York City – and Staten Island is seeing a higher caseload than any other part of the city. Chris Glorioso talks with health officials about the issue.

The variant is being blamed for a surge in cases across the United States that has seen cases double over the last three weeks following months of decline. All but two states — Maine and South Dakota — have reported case increases in the past two weeks. While hospitalizations and daily deaths remain comparably low, those are lagging indicators and could rise as delta spreads in unvaccinated areas.

In New York City, the new seven-day case average this week is up 62% from the seven-day average the four weeks prior, city health data shows. Last week, that average was up just 32% in the same time frame. Hospitalization and daily death averages are both down in the latest period of study versus the previous week.

Existing vaccines are expected to protect people against delta and other variants of concern that have emerged, but with just about 68% of U.S. adults having received at least one vaccine dose and less than 60% fully immunized, delta’s heightened transmissibility and associated risk has renewed concerns.

In New York City, where state data shows almost 65% of the adult population is fully vaccinated and more than 70% have had at least one shot, officials are warning of delta and doubling down on their message to get vaccinated with a sense of urgency that has been absent from the mayor’s briefings the last month.

“We see overwhelmingly people have done the right thing,” Mayor Bill de Blasio said when asked Friday on his weekly radio segment on WNYC whether restrictions need to be reinstated. “What’s working for us is to constantly report the facts as we’re seeing them, and if we see something we need to change we’ll call people to arms.”

De Blasio pointed to a preprint analysis of a new, not-yet-peer-reviewed study out of Yale and the Commonwealth Fund earlier this week that he says shows New York City’s vaccine rollout has saved more than 8,000 lives and prevent hundreds of thousands of new cases of COVID in the five boroughs.

In a lengthy Twitter thread, he outlined a number of steps the city was taking to get vaccination rates even higher, including deploying mobile sites to under-vaccinated communities, unleashing door-to-door canvassers to spread the message and offering in-home vaccination services to any eligible New Yorker who wants them.

The city has also expanded its referral bonus program for local nonprofits and focused acutely on driving private practicing doctors to encourage their patients who haven’t yet gotten vaccinated, for whatever reason, to get dosed now.

Now is an opportunity to sustain the city’s progress against COVID-19, de Blasio says, and leverage existing vaccine effectiveness to curtail delta’s spread.

Core viral rates are consistently at or near all-time pandemic lows in New Jersey as well. Like New York, the Garden State does monitor variant data, and like New York, it has seen the prevalence of delta rise throughout the state in recent weeks.

That strain is now the dominant one in New Jersey as well, accounting for 40.7% of samples sequenced in the last four weeks, up from 26.8% a week ago and 7.3% two weeks before that.

Gov. Phil Murphy has repeatedly declared new COVID cases, hospitalizations and deaths in New Jersey to reflect “a pandemic of the unvaccinated.”

Not sure how the process works? Check out our handy tri-state vaccine site finder and FAQs here

New York City and New Jersey Vaccine Providers

Click on each provider to find more information on scheduling appointments for the COVID-19 Vaccine.