The Sars-Cov-2 virus continues to throw fresh surprises at us and show new tricks, despite 16 months of intense observation by an endangered world. Even as vaccines and drugs are emerging with proof of efficacy against the virus, it periodically displays a Houdini-like talent to escape capture and sends us on a search for fresh clues to uncover its disguises.
Three such enigmas have come forth recently in the second wave of the pandemic. Variants of the virus have entered or emerged to alter the dynamics of transmission. Cases of reinfection are being reported after full vaccination which, although very few, are leading to concerns and calls for explanation. Among recovered cases of Covid-19, there have been instances of mucormycosis or ‘black fungus’ being reported. Each of these needs examination.
It is well known that viruses mutate. It is in their nature to do so, because of evolutionary biology. If they have to survive as a species, there are two conditions. They should find ways to become more infective while escaping the effect of host immunity. They should also not completely wipe out the host, lest their own species goes extinct. So there is a trade-off between infectivity and virulence based on how much of the host population is available to the virus at any time.
The virus also needs time to experiment with its mutations while in the human body. The longer it can stay, greater the opportunity. Some of the earlier mutations of Sars-Cov-2 are thought to have arisen in immunosuppressed people in whom it lingered long. Young people who overcome the virus fast with their strong immunity will not give the virus the luxury to mutate, while elderly debilitated persons do. People on prolonged ventilation provide a long period for mutation.
We now have three variants driving the spread in India. B.1.117 came from Britain. B.1.617 debuted in Maharashtra while B.1.618 emerged in Bengal. They have displaced most of the earlier variants that did not have the speed and strength of these dons. However, they too can be stalled from entering our body by protecting our nose, mouth and eyes with a mask and eye protection. We also need to prevent superspreader gatherings, which give them access to many people. Rapidly vaccinating a large number of people also slows transmission and stalls mutation.
Rapid spread of the virus in the second wave, through multiple mutations, is consistent with the view of “viruses as complex adaptive systems” (read a 2019 book of that title by Ricard Sole and Santiago F Elena). A physician friend who is fascinated by fractals and chaos theory points out that the virus buds in multiple locations and replicates towards infinity like Mandelbrot sets, named after mathematician Benoit Mandelbrot who pioneered fractal geometry. We should not let them proceed in that direction by adopting effective interventions to limit transmission and create pre-emptive immunity through vaccines.
Reinfections, occurring even after full vaccination, are also explainable. All vaccines that have been evaluated so far are systemic vaccines that produce systemic immunity to fight the virus, to prevent severe disease and death after a person is infected. Trials have evaluated them for those end points, not against infection per se. As efficacy rates for the vaccines used in India range from 62-81%, severe Covid can still occur in some vaccinated people and mild Covid can occur in more. Hospital staff, who are repeatedly subjected to high viral loads, are more likely to get ‘breakthrough’ infections. Hence the advice for even vaccinated people to wear masks till a large part of the population is vaccinated.
When many people are rapidly vaccinated in a population, such infections will become very infrequent because mild cases do not release many viruses into the circulation to infect others. We are seeing that happen in Israel, the UK and US. These countries had also used mRNA vaccines that have around 95% efficacy against severe Covid. Mucosal vaccines may be able to prevent even the initial infection but trial evidence is still awaited.
Mucormycosis is a fungal infection that affects the nose and can spread to eyes and brain. It has been seen in people who were treated with oxygen. They may have been infected by the water through which the oxygen is bubbled. It was not noted during the first wave, because steroids were not being used as standard treatment for patients on oxygen. After the RECOVERY trial showed the benefit of dexamethasone, it became standard therapy during the second wave. Tocilizumab is an even stronger immunosuppressive drug that has been used and misused during the second wave. Fungal infections tend to occur more frequently in immunosuppressed people. Such cases need to be investigated and all sources of infection must be contained.
These crossword puzzles set by the virus may be getting solved, but we should be ready for more to come as the wily virus is still to be tamed.
(Views expressed are personal)
Dr K Srinath Reddy
Cardiologist, epidemiologist and President, Public Health Foundation of India (PHFI)