A container is seen at the American Airlines' cold storage facility, the largest facility for pharmaceutical products on the East Coast, that could soon be used to store coronavirus disease (COVID-19) vaccines at Philadelphia International Airport in Philadelphia, Pennsylvania, U.S., December 4, 2020. REUTERS/Rachel Wisniewski

Boxes are seen as an American Airlines cargo plane is unloaded at Philadelphia International Airport in Philadelphia, Pennsylvania, U.S., December 4, 2020. American Airlines Cargo is the largest facility for pharmaceutical products on the East Coast, and could soon be used to store coronavirus disease (COVID-19) vaccines. REUTERS/Rachel Wisniewski

A box is pictured at the American Airlines' cold storage facility, the largest facility for pharmaceutical products on the East Coast, that could soon be used to store coronavirus disease (COVID-19) vaccines at Philadelphia International Airport in Philadelphia, Pennsylvania, U.S., December 4, 2020. REUTERS/Rachel Wisniewski

Boxes are pictured at the American Airlines' cold storage facility, the largest facility for pharmaceutical products on the East Coast, that could soon be used to store coronavirus disease (COVID-19) vaccines at Philadelphia International Airport in Philadelphia, Pennsylvania, U.S., December 4, 2020. REUTERS/Rachel Wisniewski

A worker drives a forklift at the American Airlines' cold storage facility, the largest facility for pharmaceutical products on the East Coast, that could soon be used to store coronavirus disease (COVID-19) vaccines at Philadelphia International Airport in Philadelphia, Pennsylvania, U.S., December 4, 2020. REUTERS/Rachel Wisniewski

A view inside an American Airlines cargo plane while being unloaded at Philadelphia International Airport in Philadelphia, Pennsylvania, U.S., December 4, 2020. American Airlines Cargo is the largest facility for pharmaceutical products on the East Coast, and could soon be used to store coronavirus disease (COVID-19) vaccines. REUTERS/Rachel Wisniewski

A view of the American Airlines' cold storage facility, the largest facility for pharmaceutical products on the East Coast, that could soon be used to store coronavirus disease (COVID-19) vaccines at Philadelphia International Airport in Philadelphia, Pennsylvania, U.S., December 4, 2020. REUTERS/Rachel Wisniewski

A worker drives a forklift at the American Airlines' cold storage facility, the largest facility for pharmaceutical products on the East Coast, that could soon be used to store coronavirus disease (COVID-19) vaccines at Philadelphia International Airport in Philadelphia, Pennsylvania, U.S., December 4, 2020. REUTERS/Rachel Wisniewski

A general view of the American Airlines' cold storage facility, the largest facility for pharmaceutical products on the East Coast, that could soon be used to store coronavirus disease (COVID-19) vaccines at Philadelphia International Airport in Philadelphia, Pennsylvania, U.S., December 4, 2020. REUTERS/Rachel Wisniewski

A general view of the American Airlines' cold storage facility, the largest facility for pharmaceutical products on the East Coast, that could soon be used to store coronavirus disease (COVID-19) vaccines at Philadelphia International Airport in Philadelphia, Pennsylvania, U.S., December 4, 2020. REUTERS/Rachel Wisniewski

A general view of the American Airlines' cold storage facility, the largest facility for pharmaceutical products on the East Coast, that could soon be used to store coronavirus disease (COVID-19) vaccines at Philadelphia International Airport in Philadelphia, Pennsylvania, U.S., December 4, 2020. REUTERS/Rachel Wisniewski

Roger Samways, VP of Cargo Sales at American Airlines, provides a tour of the airline's cold storage facility, the largest facility for pharmaceutical products on the East Coast, that could soon be used to store coronavirus disease (COVID-19) vaccines at Philadelphia International Airport in Philadelphia, Pennsylvania, U.S., December 4, 2020. REUTERS/Rachel Wisniewski

Roger Samways, VP of Cargo Sales at American Airlines, stands as he provides a tour of the airline's cold storage facility, the largest facility for pharmaceutical products on the East Coast, that could soon be used to store coronavirus disease (COVID-19) vaccines at Philadelphia International Airport in Philadelphia, Pennsylvania, U.S., December 4, 2020. REUTERS/Rachel Wisniewski

A general view of the American Airlines' cold storage facility, the largest facility for pharmaceutical products on the East Coast, that could soon be used to store coronavirus disease (COVID-19) vaccines at Philadelphia International Airport in Philadelphia, Pennsylvania, U.S., December 4, 2020. REUTERS/Rachel Wisniewski

A general view of the American Airlines' cold storage facility, the largest facility for pharmaceutical products on the East Coast, that could soon be used to store coronavirus disease (COVID-19) vaccines at Philadelphia International Airport in Philadelphia, Pennsylvania, U.S., December 4, 2020. REUTERS/Rachel Wisniewski

Roger Samways, VP of Cargo Sales at American Airlines, walks as he provides a tour of the airline's cold storage facility, the largest facility for pharmaceutical products on the East Coast, that could soon be used to store coronavirus (COVID-19) vaccines at Philadelphia International Airport in Philadelphia, Pennsylvania, U.S., December 4, 2020. REUTERS/Rachel Wisniewski

An American Airlines cargo plane is unloaded at Philadelphia International Airport in Philadelphia, Pennsylvania, U.S., December 4, 2020. American Airlines Cargo is the largest facility for pharmaceutical products on the East Coast, and could soon be used to store coronavirus disease (COVID-19) vaccines. REUTERS/Rachel Wisniewski

A general view of the American Airlines' cold storage facility, the largest facility for pharmaceutical products on the East Coast, that could soon be used to store coronavirus disease (COVID-19) vaccines at Philadelphia International Airport in Philadelphia, Pennsylvania, U.S., December 4, 2020. REUTERS/Rachel Wisniewski

Roger Samways, VP of Cargo Sales at American Airlines, provides a tour of the airline's cold storage facility, the largest facility for pharmaceutical products on the East Coast, that could soon be used to store coronavirus disease (COVID-19) vaccines at Philadelphia International Airport in Philadelphia, Pennsylvania, U.S., December 4, 2020. REUTERS/Rachel Wisniewski

Roger Samways, VP of Cargo Sales at American Airlines, provides a tour of the airline's cold storage facility, the largest facility for pharmaceutical products on the East Coast, that could soon be used to store coronavirus disease (COVID-19) vaccines at Philadelphia International Airport in Philadelphia, Pennsylvania, U.S., December 4, 2020. REUTERS/Rachel Wisniewski

An American Airlines cargo plane is seen before it is unloaded at Philadelphia International Airport in Philadelphia, Pennsylvania, U.S., December 4, 2020. American Airlines Cargo is the largest facility for pharmaceutical products on the East Coast, and could soon be used to store coronavirus disease (COVID-19) vaccines. REUTERS/Rachel Wisniewski

A general view of the American Airlines' cold storage facility, the largest facility for pharmaceutical products on the East Coast, that could soon be used to store coronavirus disease (COVID-19) vaccines at Philadelphia International Airport in Philadelphia, Pennsylvania, U.S., December 4, 2020. REUTERS/Rachel Wisniewski

Roger Samways, VP of Cargo Sales at American Airlines, provides a tour of the airline's cold storage facility, the largest facility for pharmaceutical products on the East Coast, that could soon be used to store coronavirus disease (COVID-19) vaccines at Philadelphia International Airport in Philadelphia, Pennsylvania, U.S., December 4, 2020. REUTERS/Rachel Wisniewski

Roger Samways, VP of Cargo Sales at American Airlines, looks on as he provides a tour of the airline's cold storage facility, the largest facility for pharmaceutical products on the East Coast, that could soon be used to store coronavirus disease (COVID-19) vaccines at Philadelphia International Airport in Philadelphia, Pennsylvania, U.S., December 4, 2020. REUTERS/Rachel Wisniewski

An American Airlines cargo plane is unloaded at Philadelphia International Airport in Philadelphia, Pennsylvania, U.S., December 4, 2020. American Airlines Cargo is the largest facility for pharmaceutical products on the East Coast, and could soon be used to store coronavirus disease (COVID-19) vaccines. REUTERS/Rachel Wisniewski

An American Airlines cargo plane lands at Philadelphia International Airport in Philadelphia, Pennsylvania, U.S., December 4, 2020. American Airlines Cargo is the largest facility for pharmaceutical products on the East Coast, and could soon be used to store coronavirus disease (COVID-19) vaccines. REUTERS/Rachel Wisniewski

An American Airlines cargo plane is unloaded at Philadelphia International Airport in Philadelphia, Pennsylvania, U.S., December 4, 2020. American Airlines Cargo is the largest facility for pharmaceutical products on the East Coast, and could soon be used to store the coronavirus disease (COVID-19) vaccines. REUTERS/Rachel Wisniewski

An American Airlines cargo plane is unloaded at Philadelphia International Airport in Philadelphia, Pennsylvania, U.S., December 4, 2020. American Airlines Cargo is the largest facility for pharmaceutical products on the East Coast, and could soon be used to store the coronavirus disease (COVID-19) vaccines. REUTERS/Rachel Wisniewski

An American Airlines cargo plane is unloaded at Philadelphia International Airport in Philadelphia, Pennsylvania, U.S., December 4, 2020. American Airlines Cargo is the largest facility for pharmaceutical products on the East Coast, and could soon be used to store coronavirus disease (COVID-19) vaccines. REUTERS/Rachel Wisniewski

An American Airlines cargo plane is unloaded at Philadelphia International Airport in Philadelphia, Pennsylvania, U.S., December 4, 2020. American Airlines Cargo is the largest facility for pharmaceutical products on the East Coast, and could soon be used to store the coronavirus disease (COVID-19) vaccines. REUTERS/Rachel Wisniewski

An American Airlines cargo plane lands at Philadelphia International Airport in Philadelphia, Pennsylvania, U.S., December 4, 2020. American Airlines Cargo is the largest facility for pharmaceutical products on the East Coast, and could soon be used to store the coronavirus disease (COVID-19) vaccines. REUTERS/Rachel Wisniewski

CEO of airport operator Flughafen Zurich AG Stephan Widrig addresses a news conference as he sits next to Councillor and economic director of the Canton of Zurich Carmen Walker Spaeh and CEO of Swiss Airlines Thomas Kluehr, as the spread of the coronavirus disease (COVID-19) continues, in Zurich, Switzerland December 4, 2020. REUTERS/Arnd Wiegmann

Councillor and economic director of the Canton of Zurich Carmen Walker Spaeh and CEO of Swiss Airlines Thomas Kluehr sit as CEO of airport operator Flughafen Zurich AG Stephan Widrig addresses a news conference, as the spread of the coronavirus disease (COVID-19) continues, in Zurich, Switzerland December 4, 2020. REUTERS/Arnd Wiegmann

Councillor and economic director of the Canton of Zurich Carmen Walker Spaeh addresses a news conference as she sits between CEO of airport operator Flughafen Zurich AG Stephan Widrig and CEO of Swiss Airlines Thomas Kluehr, as the spread of the coronavirus disease (COVID-19) continues, in Zurich, Switzerland December 4, 2020. REUTERS/Arnd Wiegmann

CEO of Swiss Airlines Thomas Kluehr addresses a news conference, as the spread of the coronavirus disease (COVID-19) continues, in Zurich, Switzerland December 4, 2020. REUTERS/Arnd Wiegmann

CEO of Swiss Airlines Thomas Kluehr addresses a news conference, as the spread of the coronavirus disease (COVID-19) continues, in Zurich, Switzerland December 4, 2020. REUTERS/Arnd Wiegmann

Councillor and economic director of the Canton of Zurich Carmen Walker Spaeh addresses a news conference next to CEO of Swiss Airlines Thomas Kluehr, as the spread of the coronavirus disease (COVID-19) continues, in Zurich, Switzerland December 4, 2020. REUTERS/Arnd Wiegmann

Councillor and economic director of the Canton of Zurich Carmen Walker Spaeh addresses a news conference next to CEO of Swiss Airlines Thomas Kluehr, as the spread of the coronavirus disease (COVID-19) continues, in Zurich, Switzerland December 4, 2020. REUTERS/Arnd Wiegmann

CEO of Swiss Airlines Thomas Kluehr addresses a news conference, as the spread of the coronavirus disease (COVID-19) continues, in Zurich, Switzerland December 4, 2020. REUTERS/Arnd Wiegmann

A photographer takes photos of an American Airlines Boeing 737 Max on the tarmac in Tulsa, Oklahoma, U.S., December 2, 2020. REUTERS/Carlo Allegri

A Boeing 737 Max engine is pictured in a maintenance hanger in Tulsa, Oklahoma, U.S., December 2, 2020. REUTERS/Carlo Allegri

A Boeing 737 Max airplane captain poses for a photo in a maintenance hanger in Tulsa, Oklahoma, U.S., December 2, 2020. REUTERS/Carlo Allegri

A Boeing 737 Max airplane captain gives an interview out the window in a maintenance hanger in Tulsa, Oklahoma, U.S., December 2, 2020. REUTERS/Carlo Allegri

The galley of a Boeing 737 Max airplane is pictured in a maintenance hanger in Tulsa, Oklahoma, U.S., December 2, 2020. REUTERS/Carlo Allegri

An empty Boeing 737 Max airplane is pictured in a maintenance hanger in Tulsa, Oklahoma, U.S., December 2, 2020. REUTERS/Carlo Allegri

A worker loads new software into the Boeing 737 Max airplane in a maintenance hanger in Tulsa, Oklahoma, U.S., December 2, 2020. REUTERS/Carlo Allegri

A worker loads new software into the Boeing 737 Max airplane in a maintenance hanger in Tulsa, Oklahoma, U.S., December 2, 2020. REUTERS/Carlo Allegri

A worker speaks to a man who loads new software into the Boeing 737 Max airplane in a maintenance hanger in Tulsa, Oklahoma, U.S., December 2, 2020. REUTERS/Carlo Allegri

A worker loads new software into the Boeing 737 Max airplane in a maintenance hanger in Tulsa, Oklahoma, U.S., December 2, 2020. REUTERS/Carlo Allegri

A worker loads new software into the Boeing 737 Max airplane in a maintenance hanger in Tulsa, Oklahoma, U.S., December 2, 2020. REUTERS/Carlo Allegri

Mechanics watch a presentation about the Boeing 737 Max airplane in a maintenance hanger in Tulsa, Oklahoma, U.S., December 2, 2020. REUTERS/Carlo Allegri

An American Airlines worker sits on an engine cowl of a Boeing 737 Max airplane in a maintenance hanger in Tulsa, Oklahoma, U.S., December 2, 2020. REUTERS/Carlo Allegri

American Airlines personnel watch a presentation about the Boeing 737 Max airplane in a maintenance hanger in Tulsa, Oklahoma, U.S., December 2, 2020. REUTERS/Carlo Allegri

Mechanics watch a presentation about the Boeing 737 Max airplane in a maintenance hanger in Tulsa, Oklahoma, U.S., December 2, 2020. REUTERS/Carlo Allegri

Mechanics watch a presentation about the Boeing 737 Max airplane in a maintenance hanger in Tulsa, Oklahoma, U.S., December 2, 2020. REUTERS/Carlo Allegri

A Mechanic watches a presentation about the Boeing 737 Max airplane in a maintenance hanger in Tulsa, Oklahoma, U.S., December 2, 2020. REUTERS/Carlo Allegri

A mechanic watches a presentation about the Boeing 737 Max airplane in a maintaince hanger in Tulsa, Oklahoma, U.S., December 2, 2020. REUTERS/Carlo Allegri

A landing gear from a Boeing 737 Max airplane is pictured in a hanger in Tulsa, Oklahoma, U.S., December 2, 2020. REUTERS/Carlo Allegri

A plug from a Boeing 737 Max airplane is pictured in a hanger in Tulsa, Oklahoma, U.S., December 2, 2020. REUTERS/Carlo Allegri

An engine from a Boeing 737 Max airplane is pictured in a hanger in Tulsa, Oklahoma, U.S., December 2, 2020. REUTERS/Carlo Allegri