Thinking Like COVID-19
We are locked in a chess game with the pandemic.
Posted Jul 07, 2020
Because viruses reproduce so quickly, they can adapt to new conditions in real time. For COVID-19, this means targeting ever younger people whose behavior exposes them to infection as recently found in Florida and elsewhere.
To outfox the pandemic, we need to think like a virus. It seems absurd to attribute thought to a humble virus that is incomplete as a life form and reproduces only in the cells of hosts. Yet, diseases do behave strategically given their dependence on hosts.
Virulence vs. Geographic Spread
Although viruses cannot reproduce independently, they evolve nevertheless. This means that they respond to changes in their environment in ways that are advantageous for their replication.
Viruses do not reproduce in the same way as other life forms because this involves cell division. Instead, upon entry to a cell, viruses use its machinery to replicate their genetic material (mostly RNA rather than DNA).
Viruses vary in how much damage they do to hosts. For example, the Ebola virus replicates very rapidly and overwhelms the host, causing death.
Virulent diseases such as Ebola are frightening and have a high mortality rate. This makes them very frightening to affected communities. Since Ebola kills its hosts, they cannot move around and spread it. So there is a trade-off between replicating quickly—that disrupts the biology of hosts—and getting spread by hosts.
At the other end of the spectrum is the common cold that kills no one but spreads very widely. Hosts are not incapacitated and go on with their daily lives spreading the infection.
Seasonal flu is more virulent than colds but less virulent than Ebola. It can afford to be more virulent because its spread is facilitated by migrating birds. The COVID-19 virus is even more virulent. Its key global vector is humans traveling in aircraft.
Coronaviruses Are Shape Changers
For a new virus, COVID-19 is unusually effective at getting transmitted, in many cases by individuals who do not yet know they are infected. It also appears to evolve with remarkable speed. In some places, it has changed to be less virulent and more mobile. The big question for virologists is whether it will evolve to be far less virulent, and more geographically mobile.
The pandemic has demonstrated a remarkable capacity for change. Initial infections involved a highly virulent strain that was more likely to infect, and kill, elderly people and those with preexisting conditions. This early strain had a low infection rate for young adults and was no match for the immune systems of children.
In recent weeks, there was a decline in the age of people being infected, suggesting that the virus is responding to human behavior.
The Falling Age of Infection and Human Behavior
Since reopening the economy, Florida has seen a dramatic decline in the average age of infections from people aged 55 to those aged 35.
Human behavior can act as a selective agent for the virus. In a scenario where the people going out and transmitting infection are mostly young, variants that infect young people have a selective advantage over those that focus on an older generation having weaker immune systems. The pattern for Florida—a mecca for beach-goers and holiday-makers—is being replicated around the country as economies open up and younger people are more socially active, often with inadequate mask-wearing and social distancing.
This thesis looks like a grim prognosticating. So, when September rolls around, can we anticipate that school openings, if they occur, precipitate a new wave of infections among the very young that up to now seemed invincible to this threat?
Is Younger Age of Infections Good or Bad?
The fact that younger people feel less vulnerable to all health threats in general, and this pandemic in particular, means that more of them visit beaches, and attend bars, wherever such venues are open. This phenomenon favors the emergence of a strain that is more effective at surmounting the immune systems of the young.
Now, no one really has much of an immune defense against the pandemic. On the surface, this would seem like very bad news.
Yet, some scientists interpret it as a positive development. For, despite the greatly increasing caseload, there is not a corresponding increase in mortality. This could mean that the conflict between disease virulence and infection rate is coming into play. If so, it is being resolved in favor of reducing lethality and increasing the infection rate.
So, we are seeing the predominance of a new strain that is less deadly but more transmissible. The bad news is that COVID-19 is not going anywhere soon. The good news is that it may become less dangerous and look more like common flu. Either way, the viruses are just an extreme case of adaptive change in the fast lane (1).
1 Barber, N. (2020). Evolution in the here and now: How adaptation and social learning explain humanity. Guilford, CT.:Prometheus/Rowman and Littlefield.