Indian airline Vistara was banned from flying to Hong Kong for two weeks earlier this month after bringing in passengers who tested positive for Covid-19 on two separate flights.
While four passengers initially tested positive on April 4th’s Delhi – Hong Kong flight, 25 people on that flight have now tested positive.
On April 4th, Vistara flight UK6395 arrived in Hong Kong from New Delhi.
So far 25 people on the flight have been confirmed with COVID-19.
Day 12 test results started coming in yesterday, accounting for 5 of the 10 imported cases. pic.twitter.com/bH8yvhxVTi
— 1B002Aaron 💉 💉 🇭🇰 (@tripperhead) April 18, 2021
Everyone on the flight would have presented a negative test to board. 5 people tested positive 12 days after the flight. This doesn’t mean that the virus was spread on the plane. India is experiencing its greatest surge in cases since the start of the pandemic – it’s not surprising that passengers on a flight out of India would be carrying the virus. And predeparture testing doesn’t guarantee someone doesn’t have the virus in small enough amounts so as not to show up at the time the test occurred.
While HEPA air filtration and downward air flow reduce the risk of transmission on a plane, making it one of the safer indoor environments, that safety is often only limited to actual travel time. United Airlines, for instance, is rare among airlines in running the auxiliary power unit on the ground during board and deplaning to take advantage of fresh air circulation and filtration. The boarding and deplaning process is otherwise a risk factor, along with time spent in the airport (at security, at the gate, and even on the jetway).
Just because passengers were seated near each other who tested positive doesn’t mean the transmission occurred on the aircraft – people seated near each other are often part of the same party (a family who may have spread it from one infected person to another) and even people seated nearby who aren’t traveling together may be queued together for boarding.
Flights like this are relatively rare but do happen, and seems consistent with how Covid-19 spreads more generally. Most people infected with the virus don’t spread it at all, even inside the home (where transmission risk is greatest, on average). Instead a small percentage of cases are responsible for superspreader events.
There have been other flights identified with clusters of passengers infected but this remains fairly uncommon and flights into places like Hong Kong, New Zealand and Australia are extensively tested. That’s good news overall.
My view throughout the pandemic is that I would rather have been flying on a plane than eating indoors at a restaurant over similar periods of time. `And of course much of the risk of travel comes from things people might do at their destination. (Skipping travel to visit a few relatives in favor of holding a large gathering at home isn’t good risk-management.) But incidents like this Vistara flight in which so many clustered cases are associated with a flight points to the importance of vaccination.