China said Thursday that it has vaccinated more than 1 billion people against COVID-19.

According to the Chinese National Health Commission, 2.16 billion doses of COVID-19 vaccines have been administered in the country so far, fully vaccinating 1.01 billion people. That accounts for more than 70% of China's population.

China's COVID-19 vaccination rate is now among the highest in the world, above the United States and Europe. The inoculation drive, however, only used domestically-made vaccines, including Sinopharm and Sinovac Biotech, both of which were approved for emergency use by the World Health Organization but have faced growing scrutiny that they may not be very effective at curbing the spread of the virus, particularly the new variants.

Despite chasing zero cases with the strictest of suppression methods, China still suffers the occasional COVID-19 outbreak. A fresh outbreak of the more contagious delta variant has been growing in the southeastern province of Fujian. Chinese authorities said the source of the outbreak there was a father who returned from Singapore in early August and transmitted the virus to his child after quarantining. The father didn't test positive for COVID-19 until 38 days after he had returned to China.

Painting the threat of the virus coming in from abroad, China has no plans to reopen its borders for the foreseeable future. Even the 2022 Winter Olympics in Beijing in February Feb is expected to be held within a very strict bubble that will make the recent Tokyo Games seem lax.

-ABC News' Karson Yiu

New York City's Heath Department announced Wednesday it is investigating a cluster of COVID-19 cases that were linked to a Labor Day weekend concert.

At least 16 people have been identified as part of the cluster linked to the Electric Zoo music festival on Randall's Island, which is located in the East River, the department said.

Eight people have been also been identified who "though likely exposed prior to attending the concert," were in attendance while potentially contagious, according to the health department.

"Anyone who attended this festival should get tested immediately, regardless of whether or not they have been vaccinated. This is especially urgent if attendees are experiencing symptoms," New York City's health commissioner, Dr. Dave Chokshi, said in a statement.

The concert's organizers had strict rules for entrance.

Attendees had to show proof of vaccination that matched their photo ID. Unvaccinated ticket holders were allowed in if they showed proof of a negative test "no more than 3 days prior to each day of attendance," according to the concert's website.

The U.S. Centers for Disease Control and Prevention's Advisory Committee on Immunization Practices (ACIP) is planning to meet on Sept. 22 and 23 and is prepared to discuss COVID-19 vaccine boosters.

This will delay the potential start date of boosters until at least late next week, past the president's planned start date for boosters on Sept. 20.

The White House acknowledged that the start date is ultimately up to the CDC and Food and Drug Administration.

The FDA advisory panel is currently scheduled to hold a public hearing on boosters for the Pfizer vaccine and will have a non-binding vote later that day.

If the FDA approves, the ACIP will discuss and vote on recommendations, such as who should get the boosters and when.

The CDC director will make the ultimate decision on the boosters following the ACIP recommendations.

-ABC News' Eric Strauss

Moderna on Wednesday released its own analysis of various studies, making the case that the company's original vaccine appears to generate the strongest protection among the three currently authorized vaccines, but also saying people who got their vaccine will also need a booster six months later.

Like Pfizer, Moderna is requesting authorization for a booster dose six months after the primary vaccination based on evidence that boosters are safe and generate immune response, and based on newly published data from its phase 3 trial showing a lower risk of breakthrough infections among people vaccinated eight months ago compared to people vaccinated 13 months ago.

Unlike Pfizer, Moderna’s third booster will be a half-dose. Moderna says its data shows that boosting with a half-shot seems to generate more than enough immune response.

-ABC News' Sony Salzman