(Natural News) Passengers on a flight bound to Hong Kong from Delhi in India tested positive for the Wuhan coronavirus (COVID-19). The positive test results came as a surprise since the 52 travelers all presented negative test results prior to boarding. Because of these new infections, Hong Kong’s strategy to keep the Wuhan coronavirus at bay – in place since January 2021 – has taken a hit.

The passengers were on board an aircraft operated by Indian carrier Vistara. From the Indian capital, the plane flew into Hong Kong on April 4. The city’s authorities did not disclose the total number of passengers, but reports surmised that there could have been as much as 188 passengers on the flight.

Hong Kong has one of the strictest entry and quarantine measures in the world. All passengers flying in must submit a negative COVID-19 test 72 hours before departure. They are also required to take another COVID-19 test upon arrival and are mandated to quarantine themselves for a three-week period.

The passengers on board the Vistara flight fulfilled all these requirements. They submitted negative COVID-19 test results prior to boarding, undertook the mandatory COVID-19 test upon arrival and isolated themselves in hotels. It was only during the three-week quarantine period that the positive results emerged.

University of Hong Kong (HKU) scientists are now working with the Hong Kong Department of Health to sequence genomes from the 52 coronavirus-positive passengers. The Hong Kong government said several cases have also been detected on flights departing from Mumbai. As such, it banned all flights from India as well as neighboring Pakistan from April 20 to May 3. Meanwhile, Vistara said it did everything it could to minimize the spread of the Wuhan coronavirus onboard its aircraft.

The Wall Street Journal talked to a number of passengers who contracted the pathogen aboard the Vistara flight, among them Rashida Fathima. The 52-year-old said she believes that she was infected on board – despite her family wearing masks while onboard and avoiding the plane’s toilet. Fathima told WSJ that some passengers were coughing repeatedly during the flight, and families walked their crying children through the airplane isles.

Scientists weigh in on how the previously uninfected passengers contracted the pathogen

A number of experts have put forward four main theories as to why the 52 passengers ended up being infected.

One theory is that the passengers could have been infected in India after their pre-flight COVID-19 test. American epidemiologist Eric Feigl-Ding said some infections “may have occurred after the initial 72-hour pre-departure time window” following the first COVID-19 test. He added: “India cases increased 60 percent each week for the last two weeks.” The south Asian country recently reported record highs in new daily infections – with 352,991 new cases reported on April 26. It previously chalked up 346,786 new cases on April 24.