CDC says thousands of people may have been exposed to COVID-19 on airplanes despite not being able to confirm a single case of viral transmission on a US plane.

Centers for Disease Control and Prevention officials believe that around 11,000 people may have been exposed to one of the 1,600 known cases of people flying while infected with the virus.

CDC spokeswoman Caitlin Shockey said that an absence of cases identified or reported is not proof that there were no cases.

Shockey said that CDC is unable to definitively point that potential cases were associated or not with exposure in air travel.

She said that "given the numerous opportunities for potential exposure associated with the entire travel journey and widespread global distribution of the virus,"

Published studies by the CDC's journal have also shown that COVID-19 may spread on airplanes in other countries.

For instance, a Vietnam Airlines passenger must have likely spread the virus to the other 14 travelers on a March 1 flight.

The flight was bound to Hanoi from London. It had 217 people aboard, according to the most recent report.

Usually, US airlines require passengers to wear masks while on the flight.

Although the CDC said that viruses do not spread easily on flights, they warned that there might be a risk of getting COVID-19 on crowded flights.

This can happen if there are other travelers onboard that are infected.

In early reports, various studies found evidence on the transmission on an airplane.

One study found transmission on an evacuation flight from Milan, Italy to Seoul, South Korea, later March.

Researchers said that around 300 people were screened for virus symptoms and given N95 masks before boarding the flight.

They were quarantined by the government or two weeks and were regularly tested when the passengers arrived.

The study found that six of the travelers tested positive at the start of the quarantine.

The said travelers were asymptomatic.

A seventh passenger tested positive on the final day of the quarantine.

The researchers said this despite previously receiving negative results.

The study found that the passenger had worn her N95 mask for the entire flight duration except when she used the bathroom.

The said passenger had been seated three rows ahead of asymptomatic travelers.

The researches said that at least one of the infected travelers used the same toilet.

The study concluded that it is "highly likely" that she caught the virus from the evacuation flight.

"Given that she did not go outside and had self-quarantined for 3 weeks alone at her home in Italy before the flight and did not use public transportation to get to the airport," the researchers were quoted

The researchers said that it is highly likely that she was infected with COVID-19 in the flight via indirect contact with an asymptomatic patient.

The United States currently has a total of 6.91 million cases of COVID-19, with 200,000 deaths.

The top three states with the greatest number of infections are California, Texas, and Florida.

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