Workers build a temporary classroom structure, so students can maintain social distancing during the coronavirus disease (COVID-19) pandemic, at Rice University in Houston, Texas, U.S., August 7, 2020. REUTERS/Adrees Latif

U.S. Military Academy (USMA) cadets wear protective face masks as they fire an M119 105 mm Howitzer artillery weapon during tactical and physical training activities as part of Cadet Summer Training at West Point, New York, U.S., August 7, 2020. REUTERS/Mike Segar

U.S. Military Academy (USMA) cadets wear protective face masks as they gather during tactical and physical training activities as part of Cadet Summer Training at West Point, New York, U.S., August 7, 2020. REUTERS/Mike Segar

A child plays in the yard at New York Public School 321 in the Park Slope neighbourhood in Brooklyn, New York, U.S., August 7, 2020. REUTERS/Brendan McDermid

New York Public School 321 is seen closed in the Park Slope neighbourhood in Brooklyn, New York, U.S., August 7, 2020. REUTERS/Brendan McDermid

New York Public School 321 is seen closed in the Park Slope neighbourhood in Brooklyn, New York, U.S., August 7, 2020. REUTERS/Brendan McDermid

Children play in the yard at New York Public School 321 in the Park Slope neighbourhood in Brooklyn, New York, U.S., August 7, 2020. REUTERS/Brendan McDermid

A child plays in the yard at New York Public School 321 in the Park Slope neighbourhood in Brooklyn, New York, U.S., August 7, 2020. REUTERS/Brendan McDermid

Children play in the yard at New York Public School 321 in the Park Slope neighbourhood in Brooklyn, New York, U.S., August 7, 2020. REUTERS/Brendan McDermid

New York Public School 321 is seen closed in the Park Slope neighbourhood in Brooklyn, New York, U.S., August 7, 2020. REUTERS/Brendan McDermid

U.S. Military Academy (USMA) cadets wear protective face masks as they gather their gear after training on the water confidence course during tactical and physical training activities as part of Cadet Summer Training at West Point, New York, U.S., August 7, 2020. REUTERS/Mike Segar

U.S. Military Academy (USMA) cadets march in formation during tactical and physical training activities as part of Cadet Summer Training at West Point, New York, U.S., August 7, 2020. REUTERS/Mike Segar

U.S. Military Academy (USMA) cadets wear protective face masks as they stand guard behind a live artillery weapon range during tactical and physical training activities as part of Cadet Summer Training at West Point, New York, U.S., August 7, 2020. REUTERS/Mike Segar

U.S. Military Academy (USMA) cadets wear protective face masks as they gather their gear following live artillery weapon firing during tactical and physical training activities as part of Cadet Summer Training at West Point, New York, U.S., August 7, 2020. REUTERS/Mike Segar

U.S. Military Academy (USMA) cadets wear protective face masks as they gather during tactical and physical training activities as part of Cadet Summer Training at West Point, New York, U.S., August 7, 2020. REUTERS/Mike Segar

U.S. Military Academy (USMA) cadets wear protective face masks as they gather their gear after training on the water confidence course during tactical and physical training activities as part of Cadet Summer Training at West Point, New York, U.S., August 7, 2020. REUTERS/Mike Segar

Weapons and helmets are seen atop the backpacks of U.S. Military Academy (USMA) cadets during tactical and physical training activities as part of Cadet Summer Training at West Point, New York, U.S., August 7, 2020. REUTERS/Mike Segar

A U.S. Military Academy (USMA) cadet wears a protective face mask while waiting to load a live 105 mm shell into an M119 105 mm Howitzer artillery weapon during tactical and physical training activities as part of Cadet Summer Training at West Point, New York, U.S., August 7, 2020. REUTERS/Mike Segar

U.S. Military Academy (USMA) cadets wear protective face masks while they wait to load live 105 mm shells into an M119 105 mm Howitzer artillery weapon during tactical and physical training activities as part of Cadet Summer Training at West Point, New York, U.S., August 7, 2020. REUTERS/Mike Segar

U.S. Military Academy (USMA) cadets wear protective face masks as they take instructions at a Call for Fire range during tactical and physical training activities as part of Cadet Summer Training at West Point, New York, U.S., August 7, 2020. REUTERS/Mike Segar

U.S. Military Academy (USMA) cadets wear protective face masks as they fire an M119 105 mm Howitzer artillery weapon during tactical and physical training activities as part of Cadet Summer Training at West Point, New York, U.S., August 7, 2020. REUTERS/Mike Segar

U.S. Military Academy (USMA) cadets wear protective face masks as they fire an M119 105 mm Howitzer artillery weapon during tactical and physical training activities as part of Cadet Summer Training at West Point, New York, U.S., August 7, 2020. REUTERS/Mike Segar

U.S. Military Academy (USMA) cadets wear protective face masks as they practice at a Call for Fire range during tactical and physical training activities as part of Cadet Summer Training at West Point, New York, U.S., August 7, 2020. REUTERS/Mike Segar

U.S. Military Academy (USMA) cadets wear protective face masks while sitting beneath camouflage netting as they take instruction at a Call for Fire range during tactical and physical training activities as part of Cadet Summer Training at West Point, New York, U.S., August 7, 2020. REUTERS/Mike Segar

U.S. Military Academy (USMA) cadets wear protective face masks as they fire live mortar shells from an artillery weapon during tactical and physical training activities as part of Cadet Summer Training at West Point, New York, U.S., August 7, 2020. REUTERS/Mike Segar

An instructor looks on (R) as a U.S. Military Academy (USMA) cadet throws a live hand grenade during tactical and physical training activities as part of Cadet Summer Training at West Point, New York, U.S., August 7, 2020. REUTERS/Mike Segar

U.S. Military Academy (USMA) cadets wear protective face masks as they fire live mortar shells from an artillery weapon during tactical and physical training activities as part of Cadet Summer Training at West Point, New York, U.S., August 7, 2020. REUTERS/Mike Segar

U.S. Military Academy (USMA) cadets wear protective face masks as they take instructions at a Call for Fire range during tactical and physical training activities as part of Cadet Summer Training at West Point, New York, U.S., August 7, 2020. REUTERS/Mike Segar TPX IMAGES OF THE DAY

U.S. Military Academy (USMA) cadets wear protective face masks as they wait in a protected bunker building to take their turns throwing live hand grenades, during tactical and physical training activities as part of Cadet Summer Training at West Point, New York, U.S., August 7, 2020. REUTERS/Mike Segar

U.S. Military Academy (USMA) cadets wear protective face masks as they fire live mortar shells from an artillery weapon during tactical and physical training activities as part of Cadet Summer Training at West Point, New York, U.S., August 7, 2020. REUTERS/Mike Segar

U.S. Military Academy (USMA) cadets wear protective face masks as they wait in a protected bunker building to take their turns throwing live hand grenades, during tactical and physical training activities as part of Cadet Summer Training at West Point, New York, U.S., August 7, 2020. REUTERS/Mike Segar

A U.S. Military Academy (USMA) cadet lands in the water after leaping from the Slide for Life, on the water confidence course, during tactical and physical training activities as part of Cadet Summer Training at West Point, New York, U.S., August 7, 2020. REUTERS/Mike Segar

A U.S. Military Academy (USMA) cadet falls to the water while leaping from the Slide for Life, on the water confidence course, during tactical and physical training activities as part of Cadet Summer Training at West Point, New York, U.S., August 7, 2020. REUTERS/Mike Segar

A U.S. Military Academy (USMA) cadet rides the Slide for Life across a pond, part of the water confidence course during tactical and physical training activities as part of Cadet Summer Training at West Point, New York, U.S., August 7, 2020. REUTERS/Mike Segar TPX IMAGES OF THE DAY

Military instructors look on as a U.S. Military Academy (USMA) cadet emerges from the water confidence course, during tactical and physical training activities as part of Cadet Summer Training at West Point, New York, U.S., August 7, 2020. REUTERS/Mike Segar

A U.S. Military Academy (USMA) cadet lands in the water after leaping from the Slide for Life, on the water confidence course, during tactical and physical training activities as part of Cadet Summer Training at West Point, New York, U.S., August 7, 2020. REUTERS/Mike Segar

A U.S. Military Academy (USMA) cadet hangs from a ropes course above a pond on the water confidence course, during tactical and physical training activities as part of Cadet Summer Training at West Point, New York, U.S., August 7, 2020. REUTERS/Mike Segar

A U.S. Military Academy (USMA) cadets work on the water confidence course during tactical and physical training activities as part of Cadet Summer Training at West Point, New York, U.S., August 7, 2020. REUTERS/Mike Segar

A U.S. Military Academy (USMA) cadet pulls himself across a ropes course above a pond on the water confidence course, during tactical and physical training activities as part of Cadet Summer Training at West Point, New York, U.S., August 7, 2020. REUTERS/Mike Segar

U.S. Military Academy (USMA) cadets wear protective face masks as they march a trail during tactical and physical training activities as part of Cadet Summer Training at West Point, New York, U.S., August 7, 2020. REUTERS/Mike Segar

A worker walks past a temporary classroom structure under construction, so students can maintain social distancing during the coronavirus disease (COVID-19) pandemic, at Rice University in Houston, Texas, U.S., August 7, 2020. REUTERS/Adrees Latif

Workers build a temporary classroom structure, so students can maintain social distancing during the coronavirus disease (COVID-19) pandemic, at Rice University in Houston, Texas, U.S., August 7, 2020. REUTERS/Adrees Latif

Workers install insulation in the ceiling of a temporary classroom structure under construction, so students can maintain social distancing during the coronavirus disease (COVID-19) pandemic, at Rice University in Houston, Texas, U.S., August 7, 2020. REUTERS/Adrees Latif

A worker guides an operator of a tractor digger during construction of a temporary classroom structures, so students can maintain social distancing during the coronavirus disease (COVID-19) pandemic, at Rice University in Houston, Texas, U.S., August 7, 2020. REUTERS/Adrees Latif

New York Public School 161 is seen closed in the Harlem neighborhood New York City, New York, U.S., August 7, 2020. REUTERS/Shannon Stapleton

The East Side Community High School is seen closed in New York City, New York, U.S., August 7, 2020. REUTERS/Shannon Stapleton

A woman walks by the closed Roberto Clemente Public School 15 in New York City, New York, U.S., August 7, 2020. REUTERS/Shannon Stapleton

The Roberto Clemente Public School 15 is seen closed in New York City, New York, U.S., August 7, 2020. REUTERS/Shannon Stapleton

Students wearing protective face masks pray for good luck before the university's national exam amid the coronavirus disease (COVID-19) outbreak, at the temple of literature in Hanoi, Vietnam August 7, 2020. REUTERS/Kham

A man wearing a protective face mask looks at a smart phone amid the coronavirus disease (COVID-19) outbreak, at the temple of literature in Hanoi, Vietnam August 7, 2020. REUTERS/Kham

Healthcare workers do a simulation for coronavirus vaccine clinical trials next week at the Faculty of Medicine at Padjadjaran University amid the COVID-19 pandemic in Bandung, Indonesia, August 6, 2020. REUTERS/Ajeng Dinar Ulfiana

A healthcare worker checks the tension of a volunteer during a simulation for coronavirus vaccine clinical trials next week at the Faculty of Medicine at Padjadjaran University amid the COVID-19 pandemic in Bandung, Indonesia, August 6, 2020. REUTERS/Ajeng Dinar Ulfiana

A pupil at Stonelaw High School receives a text message with her exam results on her mobile phon in Rutherglen, Glasgow, Scotland, Britain, August 4, 2020. Exams were cancelled in Scotland due to the coronavirus pandemic and pupils have been awarded grades based on assessment. Andy Buchanan/Pool via REUTERS

A pupil at Stonelaw High School receives a text message with her exam results on her mobile phon in Rutherglen, Glasgow, Scotland, Britain, August 4, 2020. Exams were cancelled in Scotland due to the coronavirus pandemic and pupils have been awarded grades based on assessment. Andy Buchanan/Pool via REUTERS

A pupil at Stonelaw High School receives a text message with her exam results on her mobile phon in Rutherglen, Glasgow, Scotland, Britain, August 4, 2020. Exams were cancelled in Scotland due to the coronavirus pandemic and pupils have been awarded grades based on assessment. Andy Buchanan/Pool via REUTERS

A pupil at Stonelaw High School receives a text message with her exam results on her mobile phon in Rutherglen, Glasgow, Scotland, Britain, August 4, 2020. Exams were cancelled in Scotland due to the coronavirus pandemic and pupils have been awarded grades based on assessment. Andy Buchanan/Pool via REUTERS

Deputy First Minister of Scotland and Cabinet Secretary for Education and Skills John Swinney visits Stonelaw High School on the day pupils receive their exam results, in Rutherglen, Glasgow, Scotland, Britain, August 4, 2020. Exams were cancelled in Scotland due to the coronavirus pandemic and pupils have been awarded grades based on assessment. Andy Buchanan/Pool via REUTERS

Deputy First Minister of Scotland and Cabinet Secretary for Education and Skills John Swinney visits Stonelaw High School on the day pupils receive their exam results, in Rutherglen, Glasgow, Scotland, Britain, August 4, 2020. Exams were cancelled in Scotland due to the coronavirus pandemic and pupils have been awarded grades based on assessment. Andy Buchanan/Pool via REUTERS

Deputy First Minister of Scotland and Cabinet Secretary for Education and Skills John Swinney visits Stonelaw High School on the day pupils receive their exam results, in Rutherglen, Glasgow, Scotland, Britain, August 4, 2020. Exams were cancelled in Scotland due to the coronavirus pandemic and pupils have been awarded grades based on assessment. Andy Buchanan/Pool via REUTERS

Deputy First Minister of Scotland and Cabinet Secretary for Education and Skills John Swinney visits Stonelaw High School on the day pupils receive their exam results, in Rutherglen, Glasgow, Scotland, Britain, August 4, 2020. Exams were cancelled in Scotland due to the coronavirus pandemic and pupils have been awarded grades based on assessment. Andy Buchanan/Pool via REUTERS