US needs negative Covid-19 test to fly: showing an outbreak on a flight from Dubai to New Zealand over safety

Being a doctor is one of the most common questions I have gotten through the whole pandemic, whether flying is ‘safe’.

The demand has new urgency, with more contagious variants of Covid-19 spreading around the world, and with the new US policy, which takes effect on January 26, all passengers must fly into the country within three days of their negative test for Covid- 19 to test. flight.

The answer to the question of whether flying is safe, as with most questions in this epidemic, is that it is complicated.

Outbreaks of Covid-19 on flights have been documented several times since the start of the pandemic, although it appeared to be more before masks were widely worn on aircraft. But a recent outbreak on a long-haul flight from Dubai to New Zealand highlights why flights can be from safe to unsafe, depending on a number of factors. It is also an example of why viral transmission is not so much a single event, but the result of multiple declines in safety.

New genomic data from the flight outbreak this fall sheds light on exactly how complicated the detection of the dynamics of transmission can be in any environment – even one so controlled as an international aircraft ride.

We still do not know exactly why this flight became a distribution event

On an 18-hour flight from Dubai to New Zealand last September, four passengers were infected by one other passenger who was unaware on board the flight that they were infected with Covid-19. Some have pointed to this outbreak as proof that flying is unsafe, but I think it misses a number of important points.

It is important to understand that the transfer does not just happens. It actually requires a number of protections that fall apart one after the other. This is argued in the ‘Swiss cheese model’, in which most single prevention methods cannot block all transmission, but a layered approach of multiple precautions can stop most spread.

In this particular outbreak, two of the four passengers who became infected reported during the flight. This also happened despite the test before departure. The person who brought the virus into the plane was incorrectly tested within 48 hours after the flight, whereas the negative test was actually four days prior. The people involved in the outbreak sat within four rows of each other, but not everyone in the radius later tested positive for the virus. In addition, the plane’s power unit was down for 30 minutes during a fuel supply in Kuala Lumpur, meaning the ventilation system was turned off.

All of these factors include a number of “what ifs” that we can ask about what could have prevented the broadcast – and whether improving these steps could make other flights safer.

Suppose, for example, the index case were to be tested within two or three days after the flight? It is quite possible that their infection would have been picked up and that they would never have come on board. What if the airline uses fast antigen tests at the airport, which we think are excellent at detecting people who are very contagious? The remark for this outbreak is that the index case only reported any symptoms two days after the flight, so symptoms that had climbed before or fever tests would not have had it either.

What if the passengers fell further from the index, or if the flight was shorter? We know that distance from the index case and the duration of contact during travel are both associated with a higher virus attack.

From now on, only Delta will block middle seats, and Alaska Airlines will do so in the premium division. And in the September outbreak, none of those who caught the virus on the run fell directly next to the index. Some were two rows in front, others behind.

What if the power unit was not turned off? We know that aircraft have good ventilation with HEPA filtration that can block viruses – when the system is running. But there is virtually no way to ensure that a flight for unforeseen reasons does not have to eliminate its air systems, such as maintenance problems or decoration.

Suppose the passengers and the index all wore better masks – such as KF94, KN95, elastomeric N95 or N95 masks with high filtration, which can provide better control over virus spread and personal protection? We know that these ‘hi-fi’ masks can work just as effectively as vaccines, if not better, to stop the transmission when worn correctly and in times of high risk.

When I tweeted about this outbreak, a number of people got in quickly – some said the transfer took place because the ventilation openings were down, others said because passengers did not have better masks. In the end, we do not know for sure which of these things it was; more likely, it was a combination of all.

What this also demonstrates is that it can actually be somewhat complicated to fully understand how much Covid-19 transmission occurs directly on flights and elsewhere.

We probably miss the most distribution of Covid-19 on aircraft in the US

In the case of this particular flight, New Zealand – which had a remarkably low incidence of Covid-19 – actually had a mandatory quarantine period during which passengers were in government facilities for 14 days, and this was regularly monitored. This has enabled researchers to isolate the potential transfer points to the flight or airport. However, infected passengers did not report any close contact with each other at the airport. Genomic studies helped detect the infections as they probably occurred during the flight itself, as the virus samples all had the same sex line. This level of follow-up is rare in the US.

In the United States, you can currently fly and your quarantine period and subsequent tests take place on the honor system, although the CDC recommends it. If people are not strictly in quarantine, it becomes much more difficult to know whether the transfer took place on the flight or afterwards, such as on your shares from the airport, at your family member or during another activity.

We really do not have a good understanding of how many infections occur on flights. And as aircraft become overcrowded, the spread of communities increases and new, more contagious variants of the virus increase, the chances of someone who is actively infected next to you also go up.

One proxy for this risk may be the infection rate among airline personnel, and it may be interesting and important to monitor over time. In Canada, infections and exposure to flights are much more easily documented, with an almost daily list of flights infecting passengers. Since the start of the pandemic, the country’s health officials have identified more than 3,000 flights that landed in Canada (domestic and international) on which at least one person had Covid-19. The US will benefit from this, although it should also be accompanied by rapid contact detection.

Does all this mean that flights are dangerous? Does that mean do not fly?

I would say that it ultimately depends on numerous protections that can and will sometimes be beyond our control, both for flights and for all other activities in which we participate.

I would now recommend against unnecessary travel, not only because I am worried about what happens on the flight (even though many flights end up with a low risk), but also about what happens after the flight. We have no quarantine enforcement after travel, and many people cannot get home quarantined safely. The more we move around and meet others, the more the virus spreads.

And a single negative test three days in advance will not stop it, even if it catches infections and prevents outbreaks on international flights. In fact, we need to increase all precautionary measures, especially on domestic flights. With new Covid-19 variants, even our air travel will require us to do many things right to avoid one wrong outcome.

Abraar Karan is a physician at Brigham and Women’s Hospital and Harvard Medical School. He has previously worked on the Cachid-19 response from Massachusetts and is a consultant to the Independent Panel on Pandemic Preparedness and Response. The opinions expressed here are his own.