Boxes of COVID-19 self-test kit are seen at Lepeltier primary school in La Trinite near Nice, amid the coronavirus disease (COVID-19) outbreak in France, April 26, 2021. REUTERS/Eric Gaillard

Coat hangers are seen in a corridor as schoolchildren return to classes at Lepeltier primary school in La Trinite, near Nice, amid the coronavirus disease (COVID-19) outbreak in France, April 26, 2021. REUTERS/Eric Gaillard

Schoolchildren, wearing protective face masks, return to classes at Lepeltier primary school in La Trinite, near Nice, amid the coronavirus disease (COVID-19) outbreak in France, April 26, 2021. REUTERS/Eric Gaillard

Schoolchildren gather in the playground as they return to classes at Lepeltier primary school in La Trinite, near Nice, amid the coronavirus disease (COVID-19) outbreak in France, April 26, 2021. REUTERS/Eric Gaillard

A COVID-19 self-test kit is used by school employee at Lepeltier primary school, amid the coronavirus disease (COVID-19) outbreak in La Trinite, near Nice, France, April 26, 2021. REUTERS/Eric Gaillard

Schoolchildren, wearing protective face masks, are seen in a classroom at Lepeltier primary school in La Trinite, near Nice, amid the coronavirus disease (COVID-19) outbreak in France, April 26, 2021. REUTERS/Eric Gaillard

A teacher, wearing a protecive face mask, teaches to schoolchildren in a classroom at Lepeltier primary school in La Trinite, near Nice, amid the coronavirus disease (COVID-19) outbreak in France, April 26, 2021. REUTERS/Eric Gaillard

A teacher, wearing a protecive face mask, teaches to schoolchildren in a classroom at Lepeltier primary school in La Trinite, near Nice, amid the coronavirus disease (COVID-19) outbreak in France, April 26, 2021. REUTERS/Eric Gaillard

A schoolboy gives a sample during a COVID-19 saliva test at Lepeltier primary school in La Trinite, near Nice, amid the coronavirus disease (COVID-19) outbreak in France, April 26, 2021. REUTERS/Eric Gaillard

A schoolgirl gives a sample during a COVID-19 saliva test at Lepeltier primary school in La Trinite, near Nice, amid the coronavirus disease (COVID-19) outbreak in France, April 26, 2021. REUTERS/Eric Gaillard

Schoolchildren attend a COVID-19 saliva test at Lepeltier primary school in La Trinite, near Nice, amid the coronavirus disease (COVID-19) outbreak in France, April 26, 2021. REUTERS/Eric Gaillard

A COVID-19 self-test kit is used by school employee at Lepeltier primary school, amid the coronavirus disease (COVID-19) outbreak in La Trinite, near Nice, France, April 26, 2021. REUTERS/Eric Gaillard

A COVID-19 self-test kit is used by school employee at Lepeltier primary school, amid the coronavirus disease (COVID-19) outbreak in La Trinite, near Nice, France, April 26, 2021. REUTERS/Eric Gaillard

Schoolchildren attend a COVID-19 saliva test at Lepeltier primary school in La Trinite, near Nice, amid the coronavirus disease (COVID-19) outbreak in France, April 26, 2021. REUTERS/Eric Gaillard

Schoolchildren attend a COVID-19 saliva test at Lepeltier primary school in La Trinite, near Nice, amid the coronavirus disease (COVID-19) outbreak in France, April 26, 2021. REUTERS/Eric Gaillard

Schoolchildren attend a COVID-19 saliva test at Lepeltier primary school in La Trinite, near Nice, amid the coronavirus disease (COVID-19) outbreak in France, April 26, 2021. REUTERS/Eric Gaillard

A schoolboy gives a sample during a COVID-19 saliva test at Lepeltier primary school in La Trinite, near Nice, amid the coronavirus disease (COVID-19) outbreak in France, April 26, 2021. REUTERS/Eric Gaillard

A schoolgirl gives a sample during a COVID-19 saliva test at Lepeltier primary school in La Trinite, near Nice, amid the coronavirus disease (COVID-19) outbreak in France, April 26, 2021. REUTERS/Eric Gaillard

Schoolchildren, wearing protective face masks, wait for COVID-19 saliva tests at Lepeltier primary school in La Trinite, near Nice, amid the coronavirus disease (COVID-19) outbreak in France, April 26, 2021. REUTERS/Eric Gaillard

Schoolchildren wait for COVID-19 saliva tests at Lepeltier primary school in La Trinite, near Nice, amid the coronavirus disease (COVID-19) outbreak in France, April 26, 2021. REUTERS/Eric Gaillard

French schoolchildren gather in the playground as they return to classes at Lepeltier primary school in La Trinite, near Nice, amid the coronavirus disease (COVID-19) outbreak in France, April 26, 2021. REUTERS/Eric Gaillard

French schoolchildren gather in the playground as they return to classes at Lepeltier primary school in La Trinite, near Nice, amid the coronavirus disease (COVID-19) outbreak in France, April 26, 2021. REUTERS/Eric Gaillard

French schoolchildren gather in the playground as they return to classes at Lepeltier primary school in La Trinite, near Nice, amid the coronavirus disease (COVID-19) outbreak in France, April 26, 2021. REUTERS/Eric Gaillard

Schoolchildren walk past an Afghan National Army soldier keeping watch at a checkpoint on the outskirts of Kabul, Afghanistan April 21, 2021. REUTERS/Mohammad Ismail

A man rides past schoolchildren in Shekou area of Shenzhen, Guangdong province, China April 20, 2021. REUTERS/David Kirton

Apple Inc. iPads are stored in boxes for charging before being used for online lessons at the Gymnasium Steglitz in Berlin, Germany, April 12, 2021. REUTERS/Michele Tantussi

Apple Inc. iPads are stored in boxes for charging before being used for online lessons at the Gymnasium Steglitz in Berlin, Germany, April 12, 2021. REUTERS/Michele Tantussi

School director and teacher Antje Luekemann speaks during a lesson at the Gymnasium Steglitz in Berlin, Germany, April 12, 2021. REUTERS/Michele Tantussi

School director and teacher Antje Luekemann speaks during a lesson at the Gymnasium Steglitz in Berlin, Germany, April 12, 2021. REUTERS/Michele Tantussi

School director and teacher Antje Luekemann speaks during a lesson at the Gymnasium Steglitz in Berlin, Germany, April 12, 2021. REUTERS/Michele Tantussi

Teacher Anke Wendt uses an Ipad during a streaming lesson before she distributes COVID-19 antigen tests to schoolchildren of the 10C class at the Gymnasium Steglitz in Berlin, Germany, April 12, 2021. REUTERS/Michele Tantussi

Teacher Anke Wendt uses an Ipad during a streaming lesson as she distributes COVID-19 antigen tests to schoolchildren of the 10C class at the Gymnasium Steglitz in Berlin, Germany, April 12, 2021. REUTERS/Michele Tantussi

Teacher Anke Wendt uses an Ipad during a streaming lesson as she distributes COVID-19 antigen tests to schoolchildren of the 10C class at the Gymnasium Steglitz in Berlin, Germany, April 12, 2021. REUTERS/Michele Tantussi

Teacher Anke Wendt speaks during a lesson before she distributes COVID-19 antigen tests to schoolchildren of the 10C class at the Gymnasium Steglitz in Berlin, Germany, April 12, 2021. REUTERS/Michele Tantussi

Teacher Anke Wendt uses an Ipad during a streaming lesson before she distributes COVID-19 antigen tests to schoolchildren of the 10C class at the Gymnasium Steglitz in Berlin, Germany, April 12, 2021. REUTERS/Michele Tantussi

Boxes of COVID-19 antigen tests are stored prior to be distributed to the schoolchildren of the Gymnasium Steglitz in Berlin, Germany, April 12, 2021. REUTERS/Michele Tantussi

Boxes of COVID-19 antigen tests are stored prior to be distributed to the schoolchildren of the Gymnasium Steglitz in Berlin, Germany, April 12, 2021. REUTERS/Michele Tantussi

Boxes of COVID-19 antigen tests are stored prior to be distributed to the schoolchildren of the Gymnasium Steglitz in Berlin, Germany, April 12, 2021. REUTERS/Michele Tantussi

Teacher Anke Wendt distributes COVID-19 antigen tests to schoolchildren of the 10C class at the Gymnasium Steglitz in Berlin, Germany, April 12, 2021. REUTERS/Michele Tantussi

Teacher Anke Wendt distributes COVID-19 antigen tests to schoolchildren of the 10C class at the Gymnasium Steglitz in Berlin, Germany, April 12, 2021. REUTERS/Michele Tantussi

Teacher Anke Wendt distributes COVID-19 antigen tests to schoolchildren of the 10C class at the Gymnasium Steglitz in Berlin, Germany, April 12, 2021. REUTERS/Michele Tantussi

Teacher Anke Wendt distributes COVID-19 antigen tests to the schoolchildren of the 10C class at the Gymnasium Steglitz in Berlin, Germany, April 12, 2021. REUTERS/Michele Tantussi

A teacher, wearing a protecive face mask, teaches to schoolchildren in a classroom at a private school in Saint-Sebastien-sur-Loire, as France will start its third national lockdown and shools will close for three weeks to push back a third wave of the coronavirus disease (COVID-19) infections, France, April 2, 2021. REUTERS/Stephane Mahe

Schoolchildren attend a lesson in their classroom at a private school in Saint-Sebastien-sur-Loire, as France will start its third national lockdown and shools will close for three weeks to push back a third wave of the coronavirus disease (COVID-19) infections, France, April 2, 2021. REUTERS/Stephane Mahe

Schoolchildren attend a lesson in their classroom at a private school in Saint-Sebastien-sur-Loire, as France will start its third national lockdown and shools will close for three weeks to push back a third wave of the coronavirus disease (COVID-19) infections, France, April 2, 2021. REUTERS/Stephane Mahe

Schoolchildren, wearing protective face masks, attend a lesson in their classroom at a private school in Saint-Sebastien-sur-Loire, as France will start its third national lockdown and schools will close for three weeks to push back a third wave of the coronavirus disease (COVID-19) infections, France, April 2, 2021. REUTERS/Stephane Mahe

Schoolchildren attend a lesson in their classroom at the private primary school Jeanne D'Arc in Saint-Maur-des-Fosses, near Paris, amid the coronavirus disease (COVID-19) outbreak in France, March 30, 2021. REUTERS/Gonzalo Fuentes

Schoolchildren clean their hands at the private primary school Jeanne D'Arc in Saint-Maur-des-Fosses, near Paris, amid the coronavirus disease (COVID-19) outbreak in France, March 30, 2021. REUTERS/Gonzalo Fuentes

Schoolchildren practice sport in the playground at the private primary school Jeanne D'Arc in Saint-Maur-des-Fosses, near Paris, amid the coronavirus disease (COVID-19) outbreak in France, March 30, 2021. REUTERS/Gonzalo Fuentes

Schoolchildren, wearing protective face masks, attend a lesson in their classroom at the private primary school Jeanne D'Arc in Saint-Maur-des-Fosses, near Paris, amid the coronavirus disease (COVID-19) outbreak in France, March 30, 2021. REUTERS/Gonzalo Fuentes

Schoolchildren practice sport in the playground at the private primary school Jeanne D'Arc in Saint-Maur-des-Fosses, near Paris, amid the coronavirus disease (COVID-19) outbreak in France, March 30, 2021. REUTERS/Gonzalo Fuentes

Schoolchildren attend a lesson in their classroom at the private primary school Jeanne D'Arc in Saint-Maur-des-Fosses, near Paris, amid the coronavirus disease (COVID-19) outbreak in France, March 30, 2021. REUTERS/Gonzalo Fuentes

Schoolchildren clean their hands at the private primary school Jeanne D'Arc in Saint-Maur-des-Fosses, near Paris, amid the coronavirus disease (COVID-19) outbreak in France, March 30, 2021. REUTERS/Gonzalo Fuentes

A boy wearing a dress-up costume to mark the upcoming Jewish holiday of Purim, which is a celebration of the Jews' salvation from genocide in ancient Persia, walks on a street in the ultra-Orthodox Jewish neighbourhood of Mea Shearim in Jerusalem February 24, 2021. REUTERS/Ammar Awad

Girls wearing dress-up costumes to mark the upcoming Jewish holiday of Purim, which is a celebration of the Jews' salvation from genocide in ancient Persia, walk on a pavement in the ultra-Orthodox Jewish neighbourhood of Mea Shearim in Jerusalem February 24, 2021. REUTERS/Ammar Awad TPX IMAGES OF THE DAY

Boys wearing dress-up costumes to mark the upcoming Jewish holiday of Purim, which is a celebration of the Jews' salvation from genocide in ancient Persia, walk on a pavement in the ultra-Orthodox Jewish neighbourhood of Mea Shearim in Jerusalem February 24, 2021. REUTERS/Ammar Awad

A girl wearing a dress-up costume to mark the upcoming Jewish holiday of Purim, which is a celebration of the Jews' salvation from genocide in ancient Persia, walks on a pavement in the ultra-Orthodox Jewish neighbourhood of Mea Shearim in Jerusalem February 24, 2021. REUTERS/Ammar Awad

Children wearing dress-up costumes to mark the upcoming Jewish holiday of Purim, which is a celebration of the Jews' salvation from genocide in ancient Persia, walk on a pavement in the ultra-Orthodox Jewish neighbourhood of Mea Shearim in Jerusalem February 24, 2021. REUTERS/Ammar Awad

A girl wearing a dress-up costume to mark the upcoming Jewish holiday of Purim, which is a celebration of the Jews' salvation from genocide in ancient Persia, walks to her school in Jerusalem February 24, 2021. REUTERS/Ammar Awad

Boys wearing dress-up costumes to mark the upcoming Jewish holiday of Purim, which is a celebration of the Jews' salvation from genocide in ancient Persia, pose for a picture at their school in Jerusalem February 24, 2021. REUTERS/Ammar Awad