Employees of the drugs and chemicals group Merck KGaA wait in line near a syringe marker and the letters "vaccination" in front of a vaccination centre at Merck's plant in Darmstadt, Germany, May 4, 2021, as Germany started projects involving company doctors helping in the state's vaccination campaign against the coronavirus disease (COVID-19). Arne Dedert/Pool via REUTERS

An employee of the drugs and chemicals group Merck KGaA waits in line near a syringe marker and the letters "vaccination" in front of a vaccination centre at Merck's plant in Darmstadt, Germany, May 4, 2021, as Germany started projects involving company doctors helping in the state's vaccination campaign against the coronavirus disease (COVID-19). Arne Dedert/Pool via REUTERS

An employee of the drugs and chemicals group Merck KGaA waits in line near a syringe marker and the letters "vaccination" in front of a vaccination centre at Merck's plant in Darmstadt, Germany, May 4, 2021, as Germany started projects involving company doctors helping in the state's vaccination campaign against the coronavirus disease (COVID-19). Arne Dedert/Pool via REUTERS

An employee of the drugs and chemicals group Merck KGaA waits in line near a syringe marker and the letters "vaccination" in front of a vaccination centre at Merck's plant in Darmstadt, Germany, May 4, 2021, as Germany started projects involving company doctors helping in the state's vaccination campaign against the coronavirus disease (COVID-19). Arne Dedert/Pool via REUTERS

A French Imperial Eagle with the letter N is seen on a reliquary casket of Napoleon Bonaparte, displayed in the Musee de l'Armee (Army Museum) at the Hotel des Invalides in Paris, France, April 27, 2021. Picture taken April 27, 2021. REUTERS/Sarah Meyssonnier

Al Action wears a hand lettered t-shirt reading "I Can Breathe Again" at a demonstration one day after the guilty verdicts against former Minneapolis police officer Derek Chauvin in the death of George Floyd, in Boston, Massachusetts, U.S., April 21, 2021. REUTERS/Brian Snyder

Al Action wears a hand lettered t-shirt reading "I Can Breathe Again" at a demonstration one day after the guilty verdicts against former Minneapolis police officer Derek Chauvin in the death of George Floyd, in Boston, Massachusetts, U.S., April 21, 2021. REUTERS/Brian Snyder TPX IMAGES OF THE DAY

Knitted figures of Britain's Queen Elizabeth and Prince Philip, her husband who died at the age of 99, are pictured on top of a letter box on the day of the funeral of the Prince, in Windsor, near London, Britain April 17, 2021. REUTERS/Peter Cziborra

Knitted figures of Britain's Queen Elizabeth and Prince Philip, her husband who died at the age of 99, are pictured on top of a letter box on the day of the funeral of the Prince, in Windsor, near London, Britain April 17, 2021. REUTERS/Peter Cziborra

Knitted figures of Britain's Queen Elizabeth and Prince Philip, her husband who died at the age of 99, are pictured on top of a letter box in Windsor, near London, Britain, April 16, 2021. REUTERS/Phil Noble

Knitted figures, including those of Britain's Queen Elizabeth and Prince Philip, her husband who died at the age of 99, are pictured on top of a letter box in Windsor, near London, Britain, April 16, 2021. REUTERS/Phil Noble

Knitted figures of Britain's Queen Elizabeth and Prince Philip, her husband who died at the age of 99, are pictured on top of a letter box in Windsor, near London, Britain, April 16, 2021. REUTERS/Phil Noble

Knitted figures of Britain's Queen Elizabeth and Prince Philip, her husband who died at the age of 99, are pictured on top of a letter box in Windsor, near London, Britain, April 16, 2021. REUTERS/Phil Noble

Knitted figures of Britain's Queen Elizabeth and Prince Philip, her husband who died at the age of 99, are pictured on top of a letter box in Windsor, near London, Britain, April 16, 2021. REUTERS/Phil Noble

LG phones are displayed in shape of letters "L" and "G", in Anyang, South Korea April 12, 2021. Picture taken April 12, 2021. REUTERS/Daewoung Kim

Former Israeli army sniper David Roytman, who uses live-fire ranges as studios and guns instead of brushes to create his artworks, peels off a Hebrew letter as he works on one of his pieces at a shooting range in Ashdod, Israel April 11, 2021. Picture taken April 11, 2021. REUTERS/Amir Cohen

A girl holds a letter in front of flowers at Hillsborough Castle after Britain's Prince Philip, husband of Queen Elizabeth, died at the age of 99, in Hillsborough, Northern Ireland, April 10, 2021. REUTERS/Jason Cairnduff

A banner reading "I do not want to die" pictures a complaint letter filed by a woman to a local prosecutor's office, detailing the abuse and violence she suffered from her partner, as part of a campaign against Turkey's withdrawal from Istanbul Convention, an international accord designed to protect women, in Istanbul, Turkey, April 5, 2021. REUTERS/Dilara Senkaya

A banner reading "I do not want to die" pictures a complaint letter filed by a woman to a local prosecutor's office, detailing the abuse and violence she suffered from her partner, as part of a campaign against Turkey's withdrawal from Istanbul Convention, an international accord designed to protect women, in Istanbul, Turkey, April 5, 2021. REUTERS/Dilara Senkaya

Firefighters, colleagues of Djordje Vukicevic who picked up Cristiano Ronaldo's armband which the Portugal captain threw on the pitch after his goal was disallowed in a World Cup qualifier against Serbia, stand at the Belgrade's firefighting brigade headquarters, Serbia, April 1, 2021. Djordje and his colleagues put up for a charity auction the blue armband with a white letter C to collect money for the treatment of a 6-month-old Gavrilo Djurdjevic from Serbia who is suffering from spinal muscular atrophy. REUTERS/Marko Djurica

Djordje Vukicevic, duty firefighter who picked up Cristiano Ronaldo's armband which the Portugal captain threw on the pitch after his goal was disallowed in a World Cup qualifier against Serbia, sits in a fire truck at the Belgrade's firefighting brigade headquaters, Serbia, April 1, 2021. Djordje and his colleagues put up for a charity auction the blue armband with a white letter C to collect money for the treatment of a 6-month-old Gavrilo Djurdjevic from Serbia who is suffering from spinal muscular atrophy. REUTERS/Marko Djurica

Djordje Vukicevic, duty firefighter, poses with Cristiano Ronaldo's armband which the Portugal captain threw on the pitch after his goal was disallowed in a World Cup qualifier against Serbia, at the Belgrade's firefighting brigade headquaters, Serbia, April 1, 2021. Djordje and his colleagues put up for a charity auction the blue armband with a white letter C to collect money for the treatment of a 6-month-old Gavrilo Djurdjevic from Serbia who is suffering from spinal muscular atrophy. REUTERS/Marko Djurica

Djordje Vukicevic, duty firefighter, poses with Cristiano Ronaldo's armband which the Portugal captain threw on the pitch after his goal was disallowed in a World Cup qualifier against Serbia, at the Belgrade's firefighting brigade headquaters, Serbia, April 1, 2021. Djordje and his colleagues put up for a charity auction the blue armband with a white letter C to collect money for the treatment of a 6-month-old Gavrilo Djurdjevic from Serbia who is suffering from spinal muscular atrophy. REUTERS/Marko Djurica

Djordje Vukicevic, duty firefighter, poses with Cristiano Ronaldo's armband which the Portugal captain threw on the pitch after his goal was disallowed in a World Cup qualifier against Serbia, at the Belgrade's firefighting brigade headquaters, Serbia, April 1, 2021. Djordje and his colleagues put up for a charity auction the blue armband with a white letter C to collect money for the treatment of a 6-month-old Gavrilo Djurdjevic from Serbia who is suffering from spinal muscular atrophy. REUTERS/Marko Djurica

Djordje Vukicevic, duty firefighter, poses with Cristiano Ronaldo's armband which the Portugal captain threw on the pitch after his goal was disallowed in a World Cup qualifier against Serbia, at the Belgrade's firefighting brigade headquaters, Serbia, April 1, 2021. Djordje and his colleagues put up for a charity auction the blue armband with a white letter C to collect money for the treatment of a 6-month-old Gavrilo Djurdjevic from Serbia who is suffering from spinal muscular atrophy. REUTERS/Marko Djurica

Djordje Vukicevic, duty firefighter who picked up Cristiano Ronaldo's armband which the Portugal captain threw on the pitch after his goal was disallowed in a World Cup qualifier against Serbia, sits in a fire truck at the Belgrade's firefighting brigade headquaters, Serbia, April 1, 2021. Djordje and his colleagues put up for a charity auction the blue armband with a white letter C to collect money for the treatment of a 6-month-old Gavrilo Djurdjevic from Serbia who is suffering from spinal muscular atrophy. REUTERS/Marko Djurica

Children hold letter spelling out "Kids vs. Racism" during a rally against anti-Asian hate crimes at Hing Hay Park in the Chinatown-International District of Seattle, Washington, U.S. March 20, 2021. REUTERS/Lindsey Wasson

Commanding General District of Columbia National Guard Major General William J. Walker holds up a letter during the Senate Homeland Security and Governmental Affairs/Rules and Administration hearing to examine the January 6, 2021 attack on the U.S. Capitol on Capitol Hill in Washington, U.S. March 3, 2021. Greg Nash/Pool via REUTERS

U.S. Senator Ted Cruz (R-TX) holds up a letter from District of Columbia Mayor Muriel Bowser during the Senate Homeland Security and Governmental Affairs/Rules and Administration hearing to examine the January 6, 2021 attack on the U.S. Capitol on Capitol Hill in Washington, U.S. March 3, 2021. Greg Nash/Pool via REUTERS

Commanding General District of Columbia National Guard Major General William J. Walker holds up a letter during the Senate Homeland Security and Governmental Affairs/Rules and Administration hearing to examine the January 6, 2021 attack on the U.S. Capitol on Capitol Hill in Washington, U.S. March 3, 2021. Greg Nash/Pool via REUTERS

Photo illustration of a letter from Park View school, detailing plans for children to return to school following the coronavirus disease (COVID-19) lockdown, in Ouston, County Durham, Britain, March 1, 2021. REUTERS/Lee Smith

The lettering 'Die Mitte' ('The Centre') is seen on the lectern as the Christian Democratic Union (CDU) Secretary General Paul Ziemiak addresses a news conference after a party leadership meeting, in Berlin, Germany February 22, 2021. Tobias Schwarz/Pool via REUTERS

Letters taken down from a company logo and red paint are seen as protesters from Palestine Action and Extinction Rebellion occupy the Elbit-Ferranti factory, where they say weapons are being made, in Waterhead, Oldham, Britain February 1, 2021. REUTERS/Carl Recine

Letters taken down from a company logo and red paint are seen as protesters from Palestine Action and Extinction Rebellion occupy the Elbit-Ferranti factory, where they say weapons are being made, in Waterhead, Oldham, Britain February 1, 2021. REUTERS/Carl Recine

A souvenir medal depicting one of the first Dinars bearing Arabic letters is displayed in Cairo, Egypt January 25, 2021. REUTERS/Amr Abdallah Dalsh REFILE - CORRECTING INFORMATION

A postman sorts letters during an extended lockdown as the spread of the coronavirus disease (COVID-19) continues in Frankfurt, Germany, January 21, 2021. REUTERS/Kai Pfaffenbach

U.S. President Donald Trump welcomes 11-years-old Frank Giaccio as he cuts the Rose Garden grass at the White House in Washington, U.S., September 15, 2017. Carlos Barria: "Once in a while I have the chance to witness a natural, unscripted moment. During a typical morning in September, I got the announcement that the White House Pool would gather by the door of the Rose Garden for a photo opportunity. As it happened, President Donald Trump was planning to surprise 11-year-old Frank Giaccio - a youngster who wrote a letter to Trump offering to mow the White House lawn. Giaccio had then been invited to work for a day at the White House alongside National Park Service staff. As we waited for Trump to show up I saw that Giaccio was very focused on this job trying to cut the grass in straight lines, and not paying much attention to the group of journalists, photographers and cameramen milling around the garden. Suddenly, from the other side of a hedge, wearing his signature long, red tie, President Trump made his appearance. As Trump approached, he began shouting to the boy above the noise of the lawnmower, but it was too loud and Giaccio was so focused on his job that he never noticed Trump. He walked right past, pushing the machine. Trump paused for a second and walked to the end of the lawn to talk to Giaccio, but again, the boy didn't stop mowing the grass. He kept going until his father rushed onto the scene to grab his attention, and then he finally stopped to greet Trump." REUTERS/Carlos Barria/File Photo SEARCH "PHOTOGRAPHERS TRUMP" FOR THIS STORY. SEARCH "WIDER IMAGE" FOR ALL STORIES. TPX IMAGES OF THE DAY.

Berlin's landmark Brandenburg Gate is illuminated with the lettering "2021"' at the start of a concert "Willkommen 2021" (Welcome 2021) amid coronavirus disease (COVID-19) restrictions in Berlin, Germany December 31, 2020. Picture taken December 31, 2020. John Macdougall/Pool via REUTERS

A security staff wears a face mask with lettering 'Happy New Year 2021' during a concert 'Willkommen 2021' (Welcome 2021) amid coronavirus disease (COVID-19) restrictions in Berlin, Germany January 1, 2021. John Macdougall/Pool via REUTERS

Berlin's landmark Brandenburg Gate is illuminated with the lettering '2021' as artists perform during a concert 'Willkommen 2021' (Welcome 2021) on New Year's Eve amid coronavirus disease (COVID-19) restrictions in Berlin, Germany December 31, 2020. John Macdougall/Pool via REUTERS

Brandenburg Gate is illuminated with the lettering '2021' at the start of a concert 'Willkommen 2021' (Welcome 2021) on New Year's Eve amid coronavirus disease (COVID-19) restrictions in Berlin, Germany December 31, 2020. John Macdougall/Pool via REUTERS

Son of Reuters cameraman Kumerra Gemechu writes a letter to his father whose picture is seen on a cell phone screen, in Addis Ababa, Ethiopia December 30, 2020. REUTERS/Stringer

A sign with lettering "CLOSED" is pictured in a shop window at the city center, amid the coronavirus disease (COVID-19) pandemic on the days of lockdown, in Berlin, Germany, December 17, 2020. REUTERS/Annegret Hilse

A sign with lettering "CLOSED" is pictured in a shop window at the city center, amid the coronavirus disease (COVID-19) pandemic on the days of lockdown, in Berlin, Germany, December 17, 2020. REUTERS/Annegret Hilse

A sign with lettering "CLOSED" is pictured in a shop window at the city center, amid the coronavirus disease (COVID-19) pandemic on the days of lockdown, in Berlin, Germany, December 17, 2020. REUTERS/Annegret Hilse

A sign with lettering "CLOSED" is pictured in a shop window at the city center, amid the coronavirus disease (COVID-19) pandemic on the days of lockdown, in Berlin, Germany, December 17, 2020. REUTERS/Annegret Hilse

A combination picture shows Santa Claus Limachem Cherem, 64, who runs a school for Santas in Rio de Janeiro, posing for photographs in his everyday clothing and dressed as Santa, and holding a letter with Christmas wishes, at a studio where he does online interactions with children and records videos, amid the coronavirus disease (COVID-19) pandemic, in Rio de Janeiro, Brazil, November 25, 2020. Cherem encourages people reach out to each other. "Get on the phone, send messages, it doesn't cost much with the internet," he said. "Since we can't hug in person, send a message of peace to a friend. He needs it, while he is at home." REUTERS/Ricardo Moraes SEARCH "GLOBAL SANTA" FOR THIS STORY. SEARCH "WIDER IMAGE" FOR ALL STORIES. TPX IMAGES OF THE DAY

Santa Claus Limachem Cherem, 64, who runs a school for Santas in Rio de Janeiro, holds a letter at a studio where he does online interactions with children and records videos, amid the coronavirus disease (COVID-19) outbreak, in Rio de Janeiro, Brazil, November 25, 2020. Cherem encourages people reach out to each other. "Get on the phone, send messages, it doesn't cost much with the internet," he said. "Since we can't hug in person, send a message of peace to a friend. He needs it, while he is at home." REUTERS/Ricardo Moraes SEARCH "GLOBAL SANTA" FOR THIS STORY. SEARCH "WIDER IMAGE" FOR ALL STORIES

A Farmers to Families food box contains a letter with U.S. President Donald Trump's signature at Christ Chapel in Woodbridge, Virginia, U.S., December 14, 2020. REUTERS/Erin Scott

A bicycle with the lettering "Corona" is seen at the city center amid the coronavirus disease (COVID-19) outbreak, in Senftenberg, Germany, December 11, 2020. REUTERS/Annegret Hilse

The mutations that give rise to new strains occur when the SARS-CoV-2 virus makes copies of itself inside a new host. The virus’ genome is a complete set of genetic instructions that is written in 30,000 “letters” of code.

Kevin Schmiegel, CEO, Operation Gratitude, holds up a letter, showing incoming first lady Jill Biden, what will go in a holiday care package for deployed troops, at the DC National Guard Armory in Washington, U.S., December 10, 2020. REUTERS/Cheriss May

Media films the car which crashed into the gate of the main entrance of the chancellery in Berlin, the office of German Chancellor Angela Merkel in Berlin, Germany, November 25, 2020. Letters written on the car read: "You damn killers of children and old people". REUTERS/Fabrizio Bensch

Firefighters remove the car which crashed into the gate of the main entrance of the chancellery in Berlin, the office of German Chancellor Angela Merkel in Berlin, Germany, November 25, 2020. Letters written on the car read: "You damn killers of children and old people". REUTERS/Fabrizio Bensch TPX IMAGES OF THE DAY

A mailbox for letters to Santa Claus is pictured at a Christmas Tree Farm, amidst the outbreak of the coronavirus disease (COVID-19), in Keele, Staffordshire, Britain November 24, 2020. REUTERS/Carl Recine

People hold signs with letters reading "no mavericks!" as they protest against a demonstration of coronavirus skeptics, amid the coronavirus disease (COVID-19) outbreak in Leipzig, Germany November 21, 2020. REUTERS/Hannibal Hanschke

People hold signs with letters reading: "Leipzig deosn't need mavericks" as they protest against a demonstration of coronavirus skeptics, amid the coronavirus disease (COVID-19) outbreak in Leipzig, Germany November 21, 2020. REUTERS/Hannibal Hanschke?

Demonstrators spray-paint a plaque with lettering on it in front of the police headquarters during a rally in Bangkok, Thailand November 18, 2020. REUTERS/Jorge Silva

Demonstrators spray-paint a plaque with lettering on it in front of the police headquarters during a rally in Bangkok, Thailand November 18, 2020. REUTERS/Jorge Silva

Demonstrators spray-paint a plaque with lettering on it in front of the police headquarters during a rally in Bangkok, Thailand November 18, 2020. REUTERS/Jorge Silva