It might take fewer infected people to achieve Covid-19 herd immunity than previously thought — and some spots in SA are already showing signs of this happening.
Herd immunity is when a disease can’t find new people to infect in a community because enough people have become immune. This comes about from many people having been infected and thus developing antibodies, or when enough people have been vaccinated so that transmission is properly interrupted.
With no vaccine in the mix yet, the antibody road to herd immunity has had scientists working non-stop to figure out the relationship between Covid-19 and how easily reinfection occurs.
According to Prof Shabir Madhi, who sits on the Covid-19 ministerial advisory committee and who is also heading up the South African vaccine trials, SA is far from out of the woods with the pandemic.
However, “When we think about a virus in the past, the thinking was you needed to get 50%-60% to get infected before herd immunity helps break the chain of transmission,” he told TimesLIVE. “But more recent modelling indicates that they might not be the case.”
He said that in some very densely populated areas in Gauteng and the Western Cape, such as Khayelitsha, Alex and Soweto, it is “highly unlikely that 50%-60% have been infected” and is more likely “30%-40% — which has already resulted in break in transmission”.
This cannot be seen as herd immunity of the whole population, he said, but it “does explain a drop in infections in some parts of those two provinces”.
People in dense areas are highly susceptible to infection, he said, and “some evolution of community immunity” has manifested in those areas.
This notion follows in the footsteps of other recent international research along the same lines. Modellers at the University of Nottingham and the University of Sweden concluded that “herd immunity to Covid-19 could be achieved with fewer people being infected than previously estimated” after they changed the variables in their modelling.
By incorporating age and social activity level into the epidemiological models, they found that the level of community infection at which herd immunity kicks in changes from about 60% to about 43%, they said in their paper published in Science.
Prof Frank Ball from the University of Nottingham participated in the research and explains: “This reduction (to 43%) is mainly due to activity level rather than age structure. The more socially active individuals are the more likely they are to get infected, and they are also more likely to infect people if they become infected.”
He said the findings have potential consequences “for release of lockdown and suggest that individual variation (for example, in activity level) is an important feature to include in models that guide policy.”
Prof Debbie Bradshaw from the South African Medical Research Council (SAMRC) said the excess-death reports compiled at her institution show a decline in some provinces. However, she added: “I want to make the point that we are not out of the woods yet. All South Africans are urged to physically distance, wear masks and wash hands. We need to do this to protect ourselves and others, particularly vulnerable people.”
International contentions about herd immunity have swirled about Sweden, which did not adopt a strong lockdown approach.
Since then, it has been held up as an example by both the pro- and anti-lockdown lobby groups: infections there have dropped dramatically, but that has come at a huge cost. According to research in The Lancet, it now has one of the highest mortality rates in Europe (even worse than the US) and only 7% of the population is testing positive for antibodies.
“In light of these findings, any proposed approach to achieve herd immunity through natural infection is not only highly unethical, but also unachievable,” it said.