How the unvaccinated threaten the vaccinated against COVID-19: A Darwinian perspective

Imai et al. (1) characterized yet another variant of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus responsible for COVID-19, this one originating in Brazil. The good news is that it appears that currently available vaccines should still offer protection against this variant. However, what about the next variation, the one we haven’t seen yet? Will we always be protected?

In 1859, Charles Darwin published About the origin of species (2), in which he outlined the principles of natural selection and survival of the fittest. The world currently has the unfortunate opportunity to see the evolutionary principles Darwin enumerated play out in real time, in the human population’s interactions with SARS-CoV-2. The world could easily have skipped this unpleasant lesson, had it not been for such a large number of the human population refusing to be vaccinated against this disease.

SARS-CoV-2 has been shown to mutate into many variants of the original agent (3). A pool of unvaccinated individuals provides a reservoir for the virus to continue to grow and multiply, and therefore more opportunities for such variants to emerge. When this occurs in the context of a widely vaccinated population, natural selection will favor a variant resistant to the vaccine.

So far, we have been fortunate that the variants that have emerged can still be somewhat controlled by current vaccines, possibly because these variants have evolved in mostly unvaccinated populations and have not been subjected to the selective pressure of having to develop in vaccinated hosts. However, the Delta variant has an increased frequency of breakthrough infections in vaccinees (4).

The real danger is a future variant, which will be the legacy of those people who don’t get vaccinated, providing fertile ground for the virus to continue to generate variants. A variant could arise that is resistant to current vaccines, making people who have already been vaccinated again susceptible.

The progress we have made in overcoming the pandemic will be lost. New vaccines will have to be developed. Containment and masks will again be required. Many other people currently protected, especially among the vulnerable, will die.

This dire prediction does not need to happen if universal immunization is adopted, or mandated, to protect everyone, including those who are already vaccinated.

Darwinian selection can also solve the problem with a much more cruel calculation. The unvaccinated will get sick and survive, and thus will be the equivalent of the vaccinated, or they will die and therefore be eliminated as breeding ground for the virus.

The National Archives of the United Kingdom note that in 1665, during the Black Death, “to prevent the disease from spreading, a victim was locked in their house with all his family, sentencing them all to death” (5). Vaccinations offer a much more humane response to prevent the spread of this disease. The way forward is in the hands of the unvaccinated and the political will of the authorities.

• Copyright © 2021 the Author (s). Published by PNAS.