“Study that found vaccines that don’t prevent viral transmission may accelerate evolution of more virulent strains could mean leading vaccine candidates may make COVID crisis worse.”
“Natural selection is the phenomenon where only the fittest individuals in an environment will survive. “Individuals” in this context can refer to any type of organism — from humans to bacteria and viruses — but the context here is the survival of viruses.
When a virus infects a population of humans, only those viruses that have a living human host will survive. If a virus is so pathogenic that it kills the human it infected, it dies too.
Therefore, mortality of the host kills the most severe forms of any virus over time. Infection rates may go up, but mortality goes down.
In a 2015 study published in PLOS Biology, researchers hypothesized that vaccination can subvert this process by allowing more virulent (i.e., more pathogenic and potentially deadly) strains of viruses to live in vaccinated hosts for prolonged time periods without killing the hosts.
These vaccinated hosts, while infected, shed and spread virus, causing further transmission of the disease.
The researchers demonstrated this hypothesis with experiments on chickens vaccinated for a disease called Marek’s Disease, a viral pathogen known to decimate poultry facilities.
Vaccinated chickens infected with more virulent strains of Marek’s Disease virus became infected and carried the infection over longer time periods. They also became “super spreaders” of the virus and transmitted the virus to unvaccinated chickens co-housed with those that received the vaccine.
Because of the higher virulence of the Marek’s Disease that was spread by the vaccinated chickens, the unvaccinated chickens usually died soon after infection.
However, the partial immunity afforded to the vaccinated chickens prolonged their survival and extended the period in which they were infectious and could continue to spread the disease.
Without vaccination, these more virulent strains of Marek’s Disease would die off with their host and would no longer circulate the virus in the population. Instead, vaccinated chickens became the perfect host to harbor the virus, allowing it to multiply and spread.
This begs the question regarding the use of vaccines that do not prevent virus transmission or are not known to prevent virus transmission.
Neither of the current COVID-19 vaccines in distribution (Pfizer and Moderna) has been shown to prevent transmission. In fact, this type of testing was not done in their rushed “warp speed” clinical studies.
Instead, both vaccines were tested for their ability to prevent more severe symptoms. In both instances, some vaccinated patients were still infected. Without prevention of transmission, these individuals spread the virus that was intended to be eradicated.
As the authors of the 2015 research state in their summary:
“When vaccines prevent transmission, as is the case for nearly all vaccines used in humans, this type of evolution towards increased virulence is blocked. But when vaccines leak, allowing at least some pathogen transmission, they could create the ecological conditions that would allow hot strains to emerge and persist.”
With the emergence of more infectious forms of COVID-19 circulating in Europe, it seems we may have created the perfect storm to prolong the pandemic, rather than curtail it — because the vaccines were developed and tested based on the original form of circulating COVID-19, not the new strains.
In our rush to create magic-bullet vaccines, have we instead created a scenario to cause more pain and suffering?”
Thank you to SC for sharing this article with us at ZMV