Airplanes as Virus Vectors: Are Three Pandemics Enough?

In the past eighteen months, humanity has already suffered three pandemics. All were variants of Covid-19: (1) the original variant Alpha, (2) the first “highly contagious” variant Delta, and (3) now the even-more-contagious Omicron.

In their rate of spread and their effect on human life, each variant caused (or is causing) a separate pandemic. All took three or fewer months to spread around the world—Omicron barely more than one month. Each caused (or is causing) a separate wave of hospitalizations and deaths. Each has stressed (or is stressing) the public-health systems in various places to capacity and beyond. And because of all the foregoing, each had (or is having) a dire effect on city, state, national, continental and global economies.

Even when governments have adamantly refused to impose lockdowns, people have done so indirectly, without orders, due to reasonable fear of infection, sickness and death. Just ask the airline, hotel, restaurant, theater, bar, gym, and brick-and-mortar retail industries.

Is there a pattern here? Each new variant has been more contagious than the last. Each new variant has caused yet another global wave of physical and economic misery. I can’t think of any scientific reason to suppose there will not be a fourth, fifth and even a sixth such wave.

The rate of viral mutation is roughly proportional to the number of people infected, multiplied by their average viral load and again by the average per-person time to recovery or death. That product will continue to increase, separately for each variant, until the total number of people infected with that variant begins to decline, whether from immunity, mass deaths, or displacement by another, even more contagious variant. We’re probably a long way from such a peak in viral evolution rate even for Delta, let alone Omicron.

So what do we do? The very first thing is to recognize the principal viral vector. It’s airplanes, or more precisely people flying on them. There is no other way that three global pandemics could have become such in less than three months each. Cars, trucks and trains don’t cross the seas, and ships move far more slowly and don’t carry many people between continents en masse anymore. So common sense suggests that air travelers are the principal vectors of our three global pandemics.

With this insight, we can see how ineffective our precautions so far have been. Masks worn on board may prevent air passengers and crew from infecting each other. But they don’t prevent infected passengers and crew from infecting others at their destinations and beyond. As for a vaccine mandate, no airline but Qantas (and then only for long-haul trans-Pacific flights) has yet imposed one on both passengers and crew. Even if all airlines did, that wouldn’t solve the problem: we now know that vaccinated people can carry the disease.

Quarantining all passengers and crew on arrival might work, but doing so would be terribly inefficient. For crew, it would make flight scheduling a nightmare. For both passengers and crew, it would meet with massive political and social resistance. (Some nations have tried this; all have gotten lots of pushback from unhappy travelers.)

So there is only one practical way that we know of now to keep infected people from flying and infecting others at their destinations. We must test all who want to board a plane, before letting them on board.

This isn’t as easy as it sounds. Not only is there an incubation period before infection produces symptoms; there is also a latency period before infection produces a testable amount of virus. Each of these periods has a range of values, likely a range of several days. But with all the studies of each variant undertaken worldwide so far, we could probably have the necessary latency data on hand within a few weeks—enough time to set up an effective testing regime.

For the sake of analysis, let’s just assume that the latency period varies from one to seven days. For a pre-boarding testing regime to work reliably, we would have to test every person boarding twice: once seven days before boarding and once immediately before.

For crew, this regime would amount to testing before every boarding, except after holidays or leaves longer than a week. Passengers would indeed have to be tested twice. And both crew and passengers would have to provide some sort of assurance of isolation from infection in between. This assurance could come in the form of detailed mandatory exposure questionnaires and/or the type of smartphone-based exposure monitoring now under development in the United States and already in use in several foreign countries.

While not without difficulty, this regime would have several advantages over the quarantines that some governments already have imposed on international air travel. First, a quarantine inconveniences everyone who flies; testing would inconvenience only those who tested positive, or who failed to provide adequate assurance against interim exposure. Second, testing before boarding would leave uninfected passengers free to go about their business or holiday on reaching their destinations, whether away from or at home. Third, once any new viral variant had been identified, tests based on the gold-standard polymerase chain reaction (PCR) could be modified immediately to pick up the new variant. That tactic wouldn’t work with vaccines, which require months of development and clinical testing for each new variant.

Air travel is undoubtedly the principal means by which Covid-19 has produced three waves of global misery so far, with no end in sight. Whether or not you call those waves separate pandemics, they are real. And there is no assurance that Omicron will be the last; what we know about viral evolution suggests the contrary.

So why don’t we try a tactic that no one has tried yet and that promises to work better and to provoke less resistance from both passengers and crew than the masking and (sporadic) quarantining that we use now? Passengers and crew could always voluntarily wear masks as they wished, whether to protect themselves, to reassure others, or both. (I would while flying, but I haven’t flown since the pandemic began because I don’t think it’s safe.)

In the US, our federal government could pick up the tab and do the lion’s share of work. The TSA could impose and carry out a testing regime as part of the boarding-security process. The federal government could provide the onsite tests and testing equipment.

With such a regime, we would have a good chance—our only real chance—of making Omicron the third and last pandemic arising from this single new virus. And the very same testing regime could prevent the global spread of any new viral pandemic as soon as the viral genome had been decoded enough for testing.

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