At least 49 passengers on a flight from New Delhi to Hong Kong have tested positive for Covid-19, according to The Straits Times.

In response, the Hong Kong health authorities have imposed a two-week ban on all flights from India, Pakistan and the Philippines, citing these locations as "extremely high-risk places".

This ban was placed in effect from Apr. 20.

Positive cases represent more than a quarter of plane capacity

According to South China Morning Post, the passengers were on a flight operated by Indian Airline Vistara, and arrived in Hong Kong on Apr. 4.

SCMP originally reported that 47 passengers tested positive for Covid-19, although ST later reported that at least 49 passengers tested positive for the virus.

The airline was operating an Airbus A321neo, which has a capacity of 188 seats, although the Hong Kong health authorities did not reveal how many passengers it was carrying.

47 passengers on Vistara flight UK6395 from New Delhi to Hong Kong on April 4th have now tested positive for COVID-19. pic.twitter.com/Mb4wCEPMPl

— Aaron Busch (@tripperhead) April 18, 2021

Even if the flight was at maximum capacity, this would mean more than a quarter of the passengers on the plane tested positive for Covid-19.

According to Forbes, this flight set a new record for the most number of positive Covid-19 cases found on a single flight.

25 travellers tested positive immediately after landing

Hotel transmission possible

Out of the 49 confirmed Covid-19 cases on the flight, only 25 travellers tested positive immediately after landing in Hong Kong, while at least 22 were only found to be positive after almost two weeks of quarantine, according to SCMP.

Hong Kong has a pre-travel testing requirement, so all of these passengers had to test negative for Covid-19 within 72 hours of their flight to Hong Kong.

Eric Feigl-Ding, an epidemiologist at the Federation of American Scientists, said that it was possible that not all of the transmission occurred during the flight, as some may have have occurred during the 72 hours window.

4) to be clear, it possible not all transmission occurred during the flight. Some may have occurred after the initial 72 hour pre departure time window after they got tested. India cases increased 60% each week for the last 2 weeks. But this is why our border testing is leaky. pic.twitter.com/7aGsVLqQ6a

— Eric Feigl-Ding (@DrEricDing) April 19, 2021

He also suggested that hotel transmission could be possible, as hotel room cross infections have been observed in Australia's hotel quarantine system.

Top image via Airbus.