US COVID-19 cases nearly 4 times higher Labor Day weekend compared to 2020

What you need to know about the COVID-19 mu variant

The World Health Organization has identified the COVID-19 mu strain as a "variant of interest."

The U.S. saw nearly four times as many COVID-19 cases over the Labor Day holiday compared to the same time period in 2020, according to Oxford University.

Data showed that on Sept. 5, 2020, the country’s weekly average number of new daily COVID-19 cases was 41,488. A year later that number rose to 163,728, nearly four times the amount. Deaths were also nearly twice as high compared to a year ago, according to the same chart.

The latest number still falls below the peak during the country’s winter surge where the weekly average number of new daily COVID-19 cases was more than 200,000 in early January 2021.

However, when it comes to daily cases, the U.S. is seeing numbers close to the winter surge. New daily cases of COVID-19 in the United States reached a staggering 229,831 on Aug. 24, according to Johns Hopkins data. The highest daily case rate recorded thus far was 293,508 in January 2021, according to data from the U.S. Centers for Disease Control and Prevention.

U.S. health officials believe the more transmissible delta variant is responsible for the latest COVID-19 surge as they keep their eye on the mu variant. The mu coronavirus variant has been detected in 49 states and 42 countries, according to estimates. The strain, also know as B.1.621, was first documented in Colombia in January 2021 but didn’t receive an official designation until Aug. 30.

According to a World Health Organization report, the mu variant is showing some signs of evading the protection imparted by COVID-19 vaccines.

The news comes as the U.S. exceeded 40 million recorded COVID-19 cases since the pandemic began this week, according to data from Johns Hopkins University. More than 4 million infections were reported in the last month, and the country has logged a total of at least 649,134 virus-related deaths.

Last week, Florida reported its highest peak in daily death rates since the start of the pandemic, surpassing previous coronavirus surges in the state, according to federal data. Data provided by the state to the U.S. Centers for Disease Control and Prevention revealed that at least eight days in August produced more daily deaths than during the last peak of the pandemic in August 2020. The typical lag times in the reporting of deaths means the true toll of the pandemic can take weeks to emerge.

Comirnaty is the first brand-name COVID-19 vaccine

Pfizer-BioNTech has named its COVID-19 vaccine "Comirnaty" after the FDA fully approved the drug.

As COVID-19 cases steadily rise in the U.S. so are vaccinations. The CDC said that nearly 75% of adults have received at least one dose of the COVID-19 vaccine. According to the CDC, 53% of the country’s total population has been fully vaccinated.

COVID-19 booster shots may be coming for at least some Americans, but already the Biden administration is being forced to scale back expectations — illustrating just how much important science still has to be worked out.

The initial plan was to offer Pfizer or Moderna boosters starting Sept. 20, contingent on authorization from U.S. regulators. But now administration officials acknowledge Moderna boosters probably won’t be ready by then — the Food and Drug Administration needs more evidence to judge them. Adding to the complexity, Moderna wants its booster to be half the dose of the original shots.

The FDA had already authorized an additional COVID-19 booster vaccine for people who have compromised immune systems.

RELATED: Fully vaccinated people half as likely to develop long-term COVID-19, study suggests

Health officials are still collecting data to see if the Johnson & Johnson COVID-19 vaccine would also require a booster.

"We also anticipate booster shots will likely be needed for people who received the Johnson & Johnson (J&J) vaccine," the statement, attributed to the CDC’s Dr. Rochelle Walensky, Dr. Anthony Fauci, the FDA’s Dr. Janet Woodcock and others, said. "Administration of the J&J vaccine did not begin in the U.S. until March 2021, and we expect more data on J&J in the next few weeks. With those data in hand, we will keep the public informed with a timely plan for J&J booster shots as well."

Earlier clinical trial data, which was collected before the delta variant emerged, showed the Johnson & Johnson shot had 72% efficacy in preventing COVID-19 in the U.S. Last month, the company said new data demonstrated the shot induced a strong neutralizing antibody response against the delta variant, and that protection lasted through at least eight months. The data showed the shot demonstrated an 85% effectiveness against severe disease, hospital and death.

FOX News and the Associated Press contributed to this report. This story was reported from Los Angeles.