South Africa: previous infections may explain Omicron hospitalisation rate
High levels of previous exposure to three previous waves of coronavirus infection in South Africa may explain the relatively low levels of hospitalisation and severe disease in the current outbreak of the Omicron variant, rather than the variant itself being less virulent.
The suggestion was made by the vaccine expert Shabir Madhi of the University of the Witwatersrand, who has led vaccine trials in the country. He warned that South Africa’s experience of Omicron might not be a reliable indicator for how the Omicron outbreak unfolds in other countries.
The same message was echoed by the head of the World Health Organization (WHO), Tedros Adhanom Ghebreyesus, who said it was “wrong for people to consider Omicron as mild”.
Other senior WHO officials, warning that the peak of Omicron could be weeks away as it spread rapidly, added that current evidence suggested vaccines were not failing to protect against Omicron altogether, and did offer some degree of protection.
In a lengthy interview with the Global Health Crisis Coordination Center, Madhi cited a recently completed seropositivity survey – the percentage of population who have already been infected – in Gauteng province, which has been at the centre of the Omicron outbreak, that suggested 72% had experienced a previous infection of coronavirus.
That is well over three times the rate of previous infections detected by a similar survey during the Beta variant outbreak a year ago where seropositivity was 20%.
While Madhi said emerging evidence pointed to the fact that Omicron was both more infectious and more able to evade antibody protection, he suggested other mechanisms at work in acquired immunity through infection could explain the lower levels of hospitalisations and severe illness.
While the UK has a seropositivity rate above 90%, South Africa’s experience may be very different to the UK’s in terms of the Omicron, with the UK having an older population and different vulnerabilities to disease.
Madhi’s comments came as a second major South African health insurer, Discovery Health, reported fewer cases of severe illness than earlier variants of the coronavirus, reporting that in 211,000 positive coronavirus cases the risk of hospital admissions among adults was 29% lower than in the initial pandemic wave that emerged in March 2020.
“The evolution of the Omicron variant is coming at a very different stage of the pandemic,” said Madhi. “That is important to keep at the back of our minds when we see what is unfolding in South Africa and what we might see in other settings, which might have a very different epidemiology.”
“In the South African much of the immunity that currently exists is largely because of the prior infection that has taken place during the first three waves,” he added. “In a survey that fortuitously just ended in [Gauteng province] on Friday what we demonstrate is that the seropositivity in Gauteng is about 72%.
“That is important to keep in the back of our mind when we see what is unfolding in South Africa and what we might expect in other settings.”
Addressing the issue of whether Omicron is “milder” than other previous variants, Madhi said the high levels of previous exposure meant that experts were “simply unable to make a meaningful head-to-head comparison of virulence with Omicron in comparison with the other variants.
“[That is] imply because of the underpinning of immunity that currently exists which is different to what existed in the past, and that immunity is going to bring about some change in the clinical course of the infection, including the likelihood of infection progressing to severe disease.”
“What is quite fascinating is that taking the rate of infection per 100,000 and comparing that to the hospitalisation rate as well as the death rate, the hospitalisation rate is much more muted compared with what was the equivalent case rate in the first three waves that transpired.
“So it tells us something is at play when the high force of infections with Omicron is not materialising in terms of severe disease and deaths in large numbers.”
Citing evidence of Omicron’s ability to evade antibody protection he suggested data was “congregating” that immunity from T cells might be driving protection against more severe disease.
With global attention closely focused on how South Africa’s Omicron outbreak is unfolding, some media reports have suggested the first evidence that Omicron cases in South Africa might be flattening. The reports, based on daily rather than more reliable weekly figures, appeared to focus on fluctuations on reporting of cases in Gauteng rather than South Africa more widely.
Contradicting those claims was reporting from the country’s National Institute for Communicable Diseases, which on Monday suggested Covid infections – both Delta and Omicron – were continuing to gather momentum, with KwaZulu-Natal Department of Health saying the province was recording more than 2,000 new cases a day, while in the Eastern Cape the Covid-19 positivity rate had increased to 17.8%.
Madhi’s argument appears to have the support of some other experts. Tulio de Oliveira, who runs two gene-sequencing institutes in South Africa, told CBS over the weekend: “You have large pockets of population immunity … We’re going to have to tease apart if the mild cases are due to young people getting infected or if the previous population immunity from infection and vaccination are responsible for decreasing the number of hospitalised individuals.”
According to the WHO other African countries are also contributing to a massive rise in Covid cases over the last week, but the number of deaths, for now at least, is lower than with previous waves.
The 83% surge means, however, that the continent will not get 70% of people fully vaccinated – considered essential to halt the pandemic – until August 2024.
“We are cautiously optimistic that deaths and severe illness will remain low in the current wave,” said Dr Matshidiso Moeti, WHO’s Regional Director for Africa. “But slow vaccine rollout in Africa means both will be much higher than they should be.”
- https://www.theguardian.com/world/2021/ ... ation-rate
So, in other words, words like natural and immunity, South Africa with a low vaccination rate and high natural immunity rate has made the Omicron variant deceptively less severe than it could be to highly vaccinated populations, who will require booster shots to manage it.
Quite literally what Geert Vanden Bossche has predicted. If this is true, then there's your depopulation scenario right there. And Australia would be fucked. 90% vaccination rate with almost no prior infection.
