ATTACK AND DEFENSE: "... It is the success or failure of our natural immune defenses that will determine the outcome of our future encounters with SARS-CoV-2 and other new viruses.".

AuthorHaseltine, William A.
PositionMEDICINE & HEALTH

VIRUSES and their hosts have been at war for hundreds of millions of years. Their battle is a classic tale of attack and defense. The virus, the predator, develops new means of attack, and humanity, the prey, responds with novel immunological defenses. So it has been for all of life; so it is with SARS-CoV-2, the virus that causes COVID-19.

Over time, the stakes and weaponry of the battle have escalated. This has been the trajectory followed by all microbes, including SARS-CoV-2. Some viral infections we have had certain success in defeating, but enough gaps remain in our pandemic control strategies for viruses to come back and flourish in new and more dangerous forms. The continual appearance of new viral variants should put to rest those evolution skeptics that doubt the power of natural selection. We only need mention the Greek alphabet of SARS-CoV-2 variants: Alpha, Beta, Gamma, Delta, Eta, Mu, Lamba, and as I write, the Omicron variants.

Given that coronaviruses have learned to adapt to infect fully immunocompetent adults repeatedly, it seems evident that SARS-CoV-2 will not disappear on its own. For those of us who pay close attention to the activity of this virus, the sudden rise of Omicron did not come as a complete surprise. What is startling is how thoroughly the virus has adapted to evade our learned (adaptive) immune defenses.

However, the body possesses another line of defense: natural immunity, also known in medical and scientific circles as innate immunity. Natural immunity precedes learned immunity and protects us from novel pathogens. Learned immunity is what allows us to react rapidly and effectively to repeated attacks from the same pathogen.

In terms of lethal potential, SARS-CoV-2 sits on a knife's edge, one unlucky mutation away from becoming substantially more dangerous. The closely related SARS-CoV-1 virus killed 10% of people infected (about four percent younger populations and about 45% of those over 70), while the more distantly related MERS still kills up to one-third of those infected. I believe it is the success or failure of our natural immune defenses that will determine the outcome of our future encounters with SARS-CoV-2 and other new viruses. Once the virus breaches this first line of defense, all bets are off regarding survival.

The increasing prevalence of the Omicron variant in countries around the world demonstrates that this virus has the ability to reinfect populations by evading the immune response generated via prior infection or vaccination. Fortunately, our vaccines reduce severe disease and death following infection by almost tenfold. Such protection is thought to be mediated...

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