A cautionary note against dropping our Covid guard
After nearly two-and-a-half years of living through the first global pandemic in close on a century, there is a pervasive sense that the worst is now over. Unlike the earlier stages of the pandemic, severe disease, hospitalisation and death are indeed low in much of the world, despite high infection rates. Political and community pressure have fostered a more relaxed approach to Covid — as UK prime minister Boris Johnson has advised, we need to plan to “live with Covid”.
Have we, at last, arrived at the end stage of the pandemic and have we now progressed to a more manageable and tolerable “endemicity” that we can “live with ”— another common cold virus, not unlike the other trivial four established endemic coronaviruses? What evidence is there to support this optimism and complacency? Does it allow us to dispense with those erstwhile irksome restrictions and punishing economic restraints?
Confidence has come from two sources — widespread population immunity and the evolution of a milder variant of the virus.
Firstly, the prevalence of antibodies in the South African population from past infection and vaccination is very high — perhaps as high as 90%. The seemingly very high level of population immunity may well have considerably ameliorated the impact of the fourth, Omicron-driven wave. It may well also reflect other more durable and effective arms of the immune system, especially cellular immunity.
Secondly, the advent of the Omicron variant was, in an odd way, “welcomed” as possibly signalling that the virus was now evolving towards a much less virulent pathogen. Indeed, several studies in laboratory animals have attested to the intrinsic mildness of Omicron infection and demonstrated its propensity to preferably infect the upper respiratory tract, the nose and the throat, rather than the lungs, unlike its predecessors. Its high transmissibility and relative mildness helped further in promoting widespread immunity in the population.
However, do these two beacons give us comfort that we are now nearing the end of the pandemic, that we can now relax our vigilance, dispense with the precautions, and return to a pre-Covid life? To look to this future realistically and responsibly, we need to probe somewhat deeper.
Let us first examine the reliance on antibody evidence of protective immunity. Undoubtedly immunity from vaccination and post-infection very effectively protected the population against severe disease, which was clearly far lower in the fourth wave. However, against infection per se, the protection was far less effective and the mutations that the Omicron virus incorporated into its structure undoubtedly afforded it the ability to scythe through widespread population immunity and overcome the immunity in even highly vaccinated people.
The immune-evasion property of Omicron was a hallmark feature of the fourth wave and demonstrated that viral adaptation to overcome immunity remains a significant threat. A further concern is how durable is the immunity, with evidence accumulating of waning of immunity in the medium term.
Secondly, we need to critically examine the suggestion that the advent of Omicron may be a signal that SARS CoV-2 is evolving towards a milder, albeit more transmissible, form of the virus. There is a long-held belief that viruses evolve towards greater transmissibility, but also diminished virulence, because it is teleologically in its “interest” to promote its spread via a relatively healthy host. Co-evolution of both virus and host towards the combination of milder illness with higher transmissibility has indeed been demonstrated in the iconic epidemic viral disease of rabbits called myxomatosis, but evidence of this with human viruses is lacking.
The intrinsic mildness of Omicron may simply be fortuitous good luck and independent of its transmissibility. In fact, Omicron is, so far, the only variant of concern (VOC) to evolve with reduced virulence — all the preceding VOCs, while progressively increasing their transmissibility, did not, in fact, reduce their virulence. Transmissibility and virulence may well be two independent and separately evolving properties of the virus. (Increasing transmissibility could conceivably go hand in hand with increased virulence where a rapidly multiplying virus could produce a high mass of virus in both upper and lower respiratory tracts and thereby increase transmissibility and cause severe disease.)
Of course, the hope is that evolutionary progression would be towards a milder, less virulent virus, but we cannot rule out the possibility of the next, or a future variant, acquiring the properties of immune evasion displayed by Omicron together with the virulence of its Delta predecessor, or even greater virulence.
What of the future? Ideally, the wish list is for a vaccine effective against all possible variants of coronavirus, past, present and future — a so-called pan-coronavirus vaccine. There has been a great deal of scientific energy put into developing and producing such a vaccine, but realistically this would not be available in the short-term future.
What is currently needed is an urgent population education effort to tackle the current mindset that the coronavirus pandemic is over. The widespread cavalier dismissal of all the Covid infection precautions, and the worrying indifference and apathy to vaccination, is a product of this unfounded wishful thinking.
The extensive spread of the virus, silently or with tolerated mild illness, will increase even further as precautions are dropped. In its wake, high levels of viral spread from human to human and, also to some extent, human to animal to human spread, promotes the chances of accumulating viral mutations expressing new and possibly nefarious properties. A recent study has demonstrated a variety of cryptic new variants in human wastewater surveillance in New York City, reflecting their circulation in the population. Clearly, we need to try to keep transmission down as much as possible to minimise the virus’s opportunity to generate new variants.
Of course, no reasonable individual would advocate returning to the harsher restrictions of the earlier past. However, what is needed is a change in prevailing community attitudes of complacency and indifference. A smart balance should be crafted which will facilitate and promote economic recovery in all sectors, while still retaining sensible, minimally invasive infection precautions.
It goes without saying that, especially in these times, the need for vaccination cannot be overstressed.