Not necessarily; before ‘Delta’ (B.1.617.2.x) , it was the ‘Alpha’ (B.1.1.7, first discovered in Kent, England) that was sweeping through populations. An even more transmissible variant, or worse yet, one with even more ability to evade immune response, could overtake it, even infecting vaccinated or previously exposed populations. Even more concerning is a variant with both an ability to evade immune response (or waning immunity over time) combined with increased virulence, because a variant with less transmissibility but a big jump in mortality and severe morbidity would still pose a major challenge. Almost all of the focus in looking at variants has been replacements (‘mutations’) in the S-protein (‘spike’) because that it what drives infectiousness, but changes in other proteins and particularly the accessory proteins coded in the open reading frame (ORF) sections of the genome can actually drive pathogenesis; a variant with a modification that increased the infection fatality rate by an order of magnitude, or one that allowed the virus to be infectious for an even longer period before exhibiting symptoms would be a whole new set of challenges.
It should be noted that this is really the first time we’ve been able to observe a truly novel zoonotic virus undergo pathological spillover into a global pandemic in real time. HIV was the last major pandemic spillover threat but the tools for rapid gene sequencing and tracking didn’t exist and even the scope of the pandemic and behavior of the virus wasn’t understood for years. Influenza A strains undergo spillback between human and animal hosts regularly, but virologists understand the behavior of influenza pretty well, and enough of the population has acquired immunity and/or seasonal vaccination across various strains that variations haven’t (yet) turned into a major pandemic threat even though epidemiologists have been warning about it for decades. The SARS-CoV(-1) virus was isolated and eliminated so quickly that it never really got a toehold (and has been a major area of pathological viral research since 2004), and MERS-CoV just isn’t transmissible enough from person-to-person contact to become a pandemic even though it is quite virulent. SARS-CoV-2 emerged completely unadapted to human hosts and with such weird behavior that virologists and epidemiologists are still scratching their heads, particularly with respect to prediction who will be most vulnerable to its effects and what the causes (multiple) of the post-infection sequelae are.
Paraphrasing Dr. Michael Osterholm (of CIDRAP), the only prediction we can make with certainty is that anyone making predictions about what will happen with future variants and how the pandemic will develop is almost certainly wrong. We’ve had experts stating that the virus will burn through the population by the middle of this year and then disappear (didn’t happen), or that we’ll achieve ‘herd immunity’ of 30%/50%/60%/70%/80%/et cetera by some date and the virus would become a mildly pathological endemic disease, or that children aren’t significant carriers and aren’t affected, et cetera, all of which have turned out to be completely wrong. People have tried to compare it to colds or flu (only affects the really old or sick), or that exposure and/or vaccination would provide ‘highly protective’ if not sterilizing immunity, or that no measures to lock down and control contagion could possibly be effective, all of which have been overstatements with broad exceptions.
This pandemic isn’t smallpox or yellow fever, but it isn’t much of a stretch to compare it to the 1918-19 H1N1 ‘bird flu’, and that pandemic followed its own trajectory without regard to predictions, and even today epidemiologists debate where that strain came from, why it emerged so rapidly, what allowed it to provoke extreme cytokine response syndrome in young healthy people, why it went through the multiple cycles, and then why it essentially went dormant and became an endemic nuisance. It was the reason that there was so much concern (bordering on panic) about the 2009 H1N1pdm09 variant that, although exceeding the P&I epidemic threshold, wasn’t nearly as virulent as feared.
Stranger