Starting Friday, New Yorkers who receive their first dose of the COVID-19 vaccine at any city-run site will get a $100 incentive.

New York Mayor Bill de Blasio made the announcement during a press briefing Wednesday.

"We will say thank you. We'll say we're really glad that you got vaccinated for yourself, for your family, for your community," de Blasio said. "And here's $100 to thank you for doing the right thing and to encourage people."

The mayor said that New Yorkers getting vaccinated will not only get the cash, they'll also be able to do "everything else that's wonderful in this city, including the amazing concerts coming up. You can't go to those concerts unless you're vaccinated."

Japan's government will put in place a coronavirus state of emergency covering three of Tokyo's neighboring prefectures and Osaka on Monday, according to public broadcaster NHK.

Tokyo and Okinawa's declarations will remain in place.

The news comes as case numbers in Japan continue to rise amid the Olympics.

As of Friday, there are 3,300 new positive cases in Tokyo, according to the Tokyo government's COVID-19 information website. Of those 3,300 cases, 88 are severe and two have turned fatal.

An internal Centers for Disease Control and Prevention brief published by the Washington Post Thursday reveals more details about why the delta variant is different to and more concerning than other strains of the coronavirus.

The CDC said the main differences between the delta variant and previous strains is that delta is highly contagious and likely more severe. Plus, breakthrough infections caused by delta may be as transmissible as unvaccinated cases.

"This is an incredibly, incredibly contagious version of virus, it's almost like a whole different virus," Dr. Ashish Jha said. "And CDC is estimating that it is probably also more deadly."

Vaccines prevent more than 90% of severe diseases, but may be less effective at preventing infection or transmission of the delta variant, the CDC said. Therefore, there could be more breakthrough infections and more community spread despite people's vaccination status.

"Current vaccines continue to provide strong protection against severe illness and death, but the delta variant is likely responsible for increased numbers of breakthrough infections -- breakthroughs that could be as infectious as unvaccinated cases," Dr. John Brownstein, an ABC News contributor, said. "This internal document highlights the challenge we all now face in combating the most transmissible variant of COVID so far."

There are now 225 positive COVID-19 cases at the Tokyo Olympics, according to a tally kept by Olympics organizers.

That is an increase of 27 cases since Thursday.

Of those cases, three of them are athletes. Two were in the Olympic Village at the time of their positive case, and one was not.

The nation's top infectious disease expert is warning that "things will get worse" in the pandemic as the rate of COVID-19 cases continues to surge.

Anthony Fauci, director of the U.S. National Institute of Allergy and Infectious Diseases, said during an interview on “This Week” that while he does not believe the pandemic is worsening to the point where lockdowns will be necessary again, "We are seeing an outbreak of the unvaccinated," based on the seven-day average, which "has gone up substantially."

"From the standpoint of illness, hospitalization, suffering and death, the unvaccinated are much more vulnerable because the vaccinated are protected from severe illness, for the most part, but when you look at the country as a whole. And getting us back to normal, the unvaccinated, by not being vaccinated, are allowing the propagation and the spread of the outbreak which ultimately impacts everybody," Fauci said.

Read more here.

-ABC News’ Molly Nagle