imperfect vaccines can make a virus more prevalent and more deadly. some questions on covid vaccines and their policy implications.
the rule of evolution is simple: make a copy of me and pass it on.
any species still around to notice is very, very good at this. that’s the test and it’s as simple as it is daunting.
this evolutionary selector creates pressures and these pressures shape evolution.
useful traits are conserved, traits that work against replication and propagation are selected against. this creates a simple evolutionary gradient for viruses: become more contagious, spread further, infect more hosts. many viruses and bacteria are incredibly good at this.
the good news is that harming the host is maladaptive. it’s like burning down your own house and your car with it. you soon have nowhere to live and no way to move around easily. so the selection process drives viruses AWAY from being deadly. ebola is a fearsome virus, but poorly evolved. it kills too quickly and spreads too slowly. that’s why outbreaks are small, rare, and (relatively) easy to manage.
people who feel sick stay home, they stop mingling and carrying the virus to where others are. it’s a built in societal and species level trait to mitigate pandemic.
but what if you could break that trait?
what if you could prevent a carrier from realizing it was infected?
well, then you’d spread virus far more effectively, wouldn’t you?
you could do A LOT of damage and the natural brake on the spread, harm, and lethality of a viral evolutionary vector would be removed. you’d supercharge a pandemic.
this is a long discussed and hypothesized problem with “leaky” vaccines.
a leaky vaccine is one that lacks sterilizing immunity. it prevents severe infection and perhaps death, but it does not stop infection and colonization by virus. so, the vaccinated become a carrier but remain unaware of it. this is a massive accelerator of disease spread and possibly/probably of overall fatality rates. you can see discussion here: (from 2015)
for those seeking an easier summary, this is a more accessible article. i strongly recommend reading the whole thing (and the study above it cites). this is another example of “science we tossed out the window this year” and is exactly the sort of thing the FDA should have been laser focused on from day one.
“But a chicken virus that represents one of the deadliest germs in history breaks from this conventional wisdom, thanks to an inadvertent effect from a vaccine. Chickens vaccinated against Marek’s disease rarely get sick. But the vaccine does not prevent them from spreading Marek’s to unvaccinated birds.
“With the hottest strains, every unvaccinated bird dies within 10 days. There is no human virus that is that hot. Ebola, for example, doesn’t kill everything in 10 days.”
In fact, rather than stop fowl from spreading the virus, the vaccine allows the disease to spread faster and longer than it normally would, a new study finds. The scientists now believe that this vaccine has helped this chicken virus become uniquely virulent.”
stop for a minute and absorb what this means. by turning the vaccinated into essentially perfect carriers of virus, it transformed them into a set of plague rats to infect the rest. a disease so deadly it would burn itself out rapidly becomes one capable of endemic spread so long at there are more vaccinated carriers around.
““Previously, a hot strain was so nasty, it wiped itself out. Now, you keep its host alive with a vaccine, then it can transmit and spread in the world,” Read said. “So it’s got an evolutionary future, which it didn’t have before.”
The virus spread to sentinel birds nine days faster if it came from a vaccinated chicken versus an unvaccinated one. In addition, sentinels died faster when exposed to vaccinated chickens versus unvaccinated chickens.
“One way to look at that experiment is that shows vaccinating birds kills unvaccinated birds. The vaccination of one group of birds leads to the transmission of a virus so hot that it kills the other birds, said Read said. “If you vaccinate the mothers, the same thing happens. The offspring are protected by the maternal antibodies of the mother and that allows the virus in the chicks to transmit before they kill the host. So they transmit and kill the other individuals.””
in such a case, your vaccine does not protect me, your vaccine puts me and everyone else at terrible risk and it is not the unvaccinated that need to be quarantined, but rather the vaccinated.
they become the dangerous vector and a monstrous amplifier of spread and risk.
not only do they spread disease unknowingly because they fail to acquire the symptoms that should tell them to reduce activity (stay home) but they also alter the evolutionary gradient of the virus by reducing the maladaptiveness of harming the host because these “superhosts” can harbor deadly virus yet not die or even become ill.
the functional line between this and viral weaponization gets perilously thin…
“leaky” vaccines pose a serious danger to populations and mistaking their societal benefit for that of a “perfect” vaccine (like measles, polio, smallpox etc) is like mistaking hemlock for gatorade. these are societally devastating, spread disease more rapidly, and breed for “hotter” deadlier disease.