hat happened was fairly simple, I’ve come to believe. It was an accident. A virus spent some time in a laboratory, and eventually it got out. SARS-CoV-2, the virus that causes COVID-19, began its existence inside a bat, then it learned how to infect people in a claustrophobic mine shaft, and then it was made more infectious in one or more laboratories, perhaps as part of a scientist’s well-intentioned but risky effort to create a broad-spectrum vaccine. SARS-2 was not designed as a biological weapon. But it was, I think, designed. Many thoughtful people dismiss this notion, and they may be right. They sincerely believe that the coronavirus arose naturally, “zoonotically,” from animals, without having been previously studied, or hybridized, or sluiced through cell cultures, or otherwise worked on by trained professionals. They hold that a bat, carrying a coronavirus, infected some other creature, perhaps a pangolin, and that the pangolin may have already been sick with a different coronavirus disease, and out of the conjunction and commingling of those two diseases within the pangolin, a new disease, highly infectious to humans, evolved. Or they hypothesize that two coronaviruses recombined in a bat, and this new virus spread to other bats, and then the bats infected a person directly — in a rural setting, perhaps — and that this person caused a simmering undetected outbreak of respiratory disease, which over a period of months or years evolved to become virulent and highly transmissible but was not noticed until it appeared in Wuhan.
We do not identify a single recurrent mutation in this set convincingly associated with increased viral transmission. Instead, recurrent mutations currently in circulation appear to be evolutionary neutral and primarily induced by the human immune system via RNA editing, rather than being signatures of adaptation. At this stage we find no evidence for significantly more transmissible lineages of SARS-CoV-2 due to recurrent mutations.
While the testing data are so opaque, using them to direct local lockdowns is unhelpful, argues Heneghan. “The testing is there to drive the test and trace strategy,” he says. “But what seems to be happening is that, as soon as we see an outbreak, there tends to be panic and over-reacting. This is a huge problem because politicians are operating in a non-evidence-based way when it comes to non-drug interventions.”
A critical factor that makes the elderly more susceptible to infectious diseases is what immunologists call “immunosenescence”: the decline in the immune system’s functionality as people age. This is also associated with an increase in the incidence of inflammatory diseases, because an elderly body tends to be in a state of chronic low-grade inflammation. This “inflamm-aging” is one reason why older people have tendencies to develop more severe forms of respiratory diseases.
The key problem with SARS-CoV-2 infection is inflammation in the respiratory tract, which can be exacerbated in individuals predisposed towards potent inflammatory responses.
Immunosenescence also results in diminished responses to vaccination. Indeed, annual flu vaccines are notoriously less effective in the elderly. This phenomenon is very important in the context of the massive efforts and funds being invested worldwide into the ultra-rapid development of vaccines for COVID-19.
The fact that elderly people do not respond well to immunizations has largely been ignored in most discussions of COVID-19 vaccines, despite this being the group in greatest need. Most of the scientific community’s experience with vaccine development for any disease has been focused on vaccinating the relatively young.
It is a common laboratory practice to propagate viruses in cell culture. While convenient, these methodologies often result in unintentional genetic alterations, which have led to adaptation and even attenuation in animal models of disease. An example is the attenuation of hantaviruses (family: Bunyaviridae, genus: Hantavirus) when cultured in vitro. In this case, viruses propagated in the natural reservoir species cause disease in nonhuman primates that closely mimics the human disease, but passaging in cell culture attenuates these viruses to the extent that do not cause any measurable disease in nonhuman primates. As efforts to develop animal models progress, it will be important to take into account the influences that culture in vitro may have on the virulence of viruses. In this review we discuss this phenomenon in the context of past and recent examples in the published literature.