Ovidiu Dugulan/iStockBy MORGAN WINSOR and MATT ZARRELL, ABC News

(NEW YORK) -- A pandemic of the novel coronavirus has now killed more than 814,000 people worldwide.

Over 23.7 million people across the globe have been diagnosed with COVID-19, the disease caused by the new respiratory virus, according to data compiled by the Center for Systems Science and Engineering at Johns Hopkins University. The actual numbers are believed to be much higher due to testing shortages, many unreported cases and suspicions that some national governments are hiding or downplaying the scope of their outbreaks.

Since the first cases were detected in China in December, the United States has become the worst-affected country, with more than 5.7 million diagnosed cases and at least 177,873 deaths.

Nearly 170 vaccine candidates are being tracked by the World Health Organization. Six of these are in crucial phase three trials, where thousands are being administered vaccine doses.

Here's how the news developed Tuesday. All times Eastern:

Aug 25, 3:20 pm
University of Miami has 141 test positive

Testing at the University of Miami showed 141 people, most of them students, tested positive for COVID-19, according to data from the school.

There were 2,627 students, faculty, staff and university vendors were tested between Aug. 16 and Aug. 22, the school posted on its new COVID-19 dashboard.

There were an additional 59 students placed in isolation and another 98 quarantined because of potential exposure to someone who was infected.

One member of the university staff was hospitalized.

Aug 25, 1:01 pm
Florida county has 158 quarantined since schools opened last week

There are 158 people who have been asked to quarantine in Seminole County, Florida, since schools opened for in-person learning last week.

The Seminole County School District opened schools on Aug. 17.

Nine schools in the district have people who are under quarantine -- the district has approximately 12 positive cases, according to public school officials.

Those in quarantine were switched to the remote learning platform until they are cleared to return to the schools, officials said.

ABC News' Rachel Katz contributed to this report.

Aug 25, 12:17 pm
New York removes 5 states from travel advisory list, adds Guam

New York Gov. Andrew Cuomo announced Tuesday that five states -- Alaska, Arizona, Delaware, Maryland and Montana -- have been removed from the Empire State's coronavirus travel advisory list, while the U.S. territory of Guam has been added.

The advisory mandates a 14-day self-quarantine for travelers arriving from areas "with significant community spread." That list now includes Alabama, Arkansas, California, Florida, Georgia, Guam, Hawaii, Iowa, Idaho, Illinois, Indiana, Kansas, Kentucky, Louisiana, Minnesota, Missouri, Mississippi, North Carolina, North Dakota, Nebraska, Nevada, Oklahoma, Puerto Rico, South Carolina, South Dakota, Tennessee, Texas, Utah, Virginia, Virgin Islands and Wisconsin.

New York state has had a rate of positive COVID-19 tests below 1% for 18 straight days, according to Cuomo, who warned "this pandemic is not over" and urged residents to "stay vigilant and be careful."

"New Yorkers made enormous sacrifices to get our numbers as low as they are today, and we don't want to give up an inch of that hard-earned progress," Cuomo said at Tuesday's press briefing. "That's why these travel advisory precautions are so important -- we don't want people who travel to states with high community spread to bring the virus back here."

Aug 25, 11:41 am
Madrid to make masks mandatory in schools for children

Face masks will be obligatory for children aged 6 and older while at schools in Spain's central capital.

Madrid's regional premier, Isabel Diaz Ayuso, announced the new measure at a press conference Tuesday, while presenting a strategy for the safe return to schools amid the coronavirus pandemic. She said class sizes will also be reduced and thousands more teachers will be hired on a temporary basis.

Diaz Ayuso noted that, if Madrid's epidemiological situation improves, face masks will only be mandatory for students aged 11 and up. The region is planning for the staggered reopening of schools in September.

With over 405,000 diagnosed cases of COVID-19 so far, Spain has the highest case count of any country in Europe. The day-to-day increase of new cases has been steadily climbing since Spain emerged from a more than three-month national lockdown in late June.

Last week, Spain's head of health emergencies, Dr. Fernando Simon, warned that "things are not going well" regarding a recent spike of infections.

"Each day, we are seeing more and more transmission," Simon said.

Aug 25, 10:29 am
South Korea closes schools across Seoul amid spike in cases

South Korea has ordered the closure of schools in the capital amid a rise in coronavirus infections there.

South Korean Education Minister Yoo Eun-hae said Tuesday that nearly 200 students and teachers have been infected in the Seoul metropolitan region over the past two weeks. Most students at kindergartens, elementary, middle and high schools will return to online learning at least until Sept. 11. Those in their final year of high school will continue to take in-person classes so their studies are not disrupted ahead of the national college exams, Yoo said.

South Korea's Centers for Disease Control and Prevention recorded 280 new cases of COVID-19 and one death on Monday, bringing the country's total to 17,945 cases and 310 deaths.

South Korea once had the largest COVID-19 outbreak outside China, where the virus first emerged, but health authorities were able to bring it under control with an extensive "trace, test and treat" strategy. Now, infections are on the rise in Seoul, home to over 25 million people, as well as in other parts of the country.

Aug 25, 9:29 am
Germany issues travel warning for Paris area

Germany has issued a travel warning for parts of France, including Paris and Marseille, due to high levels of coronavirus infection there.

The German government announced Monday that travelers returning from Ile-de-France and Provence-Alpes-Cote-d’Azur regions will be required to be tested for COVID-19 upon arrival and then must self-quarantine while awaiting the test results.

France’s national public health agency recorded 1,955 new cases of COVID-19 and 15 coronavirus-related fatalities on Monday, bringing the total to 244,854 confirmed cases and 30,528 deaths. The country is among the hardest-hit in Europe.

ABC News’ Ibtissem Guenfoud contributed to this report.

Aug 25, 7:52 am
Gaza Strip under lockdown after 1st cases of community transmission

Palestinian authorities have imposed a 48-hour lockdown on the besieged Gaza Strip after officials said a family of four tested positive for COVID-19 at a refugee camp there.

The Palestinian health ministry said another case was identified Monday at a quarantine center in Gaza, bringing the total count to five.

The cause of the cluster is unclear and authorities are working to trace it. It’s the first known instance of the novel coronavirus spreading through Gaza’s local community.

The full lockdown went into effect Monday night across the entire 140-square-mile-long coastal enclave, which shares borders with Egypt and Israel.

The Gaza Strip, a densely populated area that forms part of the so-called Occupied Palestinian Territories, is inhabited by some 2 million Palestinians, most of whom are registered refugees living in overcrowded camps. Both Egypt and Israel have imposed restrictions on movement in and out of Gaza, citing concerns over the militant group Hamas, which rules the territory and has been designated a terrorist organization by Israel and the United States.

However, a small number of Palestinians still travel to Jerusalem for routine cancer treatments, and Egypt partially lifted its blockade recently to allow Palestinians back in.

ABC News’ Nasser Atta and Guy Davies contributed to this report.

Aug 25, 6:43 am
University of Southern California reports ‘alarming increase’ in cases

The University of Southern California is reporting an “alarming increase in the number of COVID-19 cases” among students living in off-campus housing.

In a letter sent to students Monday, the university’s student health center said it had identified 43 cases in the past seven days. All cases are related to students in off-campus living environments, and more than 100 students are now in a 14-day quarantine due to exposures.

“This increase comes despite the continued state and county health guidance that significantly restricts in-person instruction and on-campus activities for universities located in counties that are on the state’s COVID-19 monitoring list, including Los Angeles County,” the letter states. “We continue to strongly discourage students from returning to the campus area until further notice.”

The private university, located in the heart of Los Angeles, kicked off its fall semester online last week, but many students remain in apartments and off-campus residences near the campus.

Aug 25, 5:48 am
New cases and deaths in US have decreased substantially, FEMA memo says

The numbers of new COVID-19 cases and new deaths in the United States have both decreased by substantial amounts in week-over-week comparisons, according to an internal memo from the Federal Emergency Management Agency obtained by ABC News Monday night.

Just five U.S. states and territories are currently in an upward trajectory of new cases, while five states are at a plateau and 46 states are going down, the memo said.

There were 300,366 new cases confirmed during the period of Aug. 17-23, a 16.2% decrease from the previous seven-day period. There were also 6,873 new deaths recorded Aug. 17-23, an 8.5% decrease from the previous week, according to the memo.

Meanwhile, the national positivity rate for COVID-19 tests ticked downward slightly from 6.4% to 5.5%, the memo said.

Oregon appears to be coming down from a peak with a 7% decrease in infections, a 19.5% decrease in hospitalizations and a 20% reduction in deaths for the week ending on Aug. 16, compared to the previous week, according to the memo.

Idaho has seen an 8.5% decrease in the seven-day case rate since Aug. 18, but a 12.2% increase in the seven-day death rate, the memo said.

In Montana, the Native American community makes up 7% of the state’s population but accounts for 18% of cases statewide and 34% of deaths, according to the memo.

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