Professor Ismail Kalla, in Pulmonology in Internal Medicine, and Professor Abdullah Laher in Emergency Medicine in the School of Clinical Medicine examined whether herd immunity was a strategy for SA in the fight against COVID-19.
“Herd immunity has been an effective tool in the fight against infectious pathogens,” said Professors Kalla and Laher. The effectiveness of herd immunity is dependent on several epidemiological principles including:
- The disease must carry a substantial health risk
- The risk of contracting the disease must be high
- The vaccine must be effective
- The vaccine must be safe.
“The COVID-19 virus fits all these principles, but there is currently no clinically proven vaccine against the virus. So, what is all the fuss regarding herd immunity for COVID-19 in the absence of an effective vaccine?
“The problem with COVID-19 is not only is it a highly infectious and contagious virus, but it’s associated with a mortality of approximately 5.8% (9 April 2020) in confirmed cases. Furthermore, crowding together of dense communities across the country, coupled with poor socioeconomic conditions, places SA at particular risk for COVID-19.”
TO LOCKDOWN OR NOT TO LOCKDOWN
While most countries' response to the emerging healthcare threat was to impose varying degrees of lockdown, the UK opted to limit new infections through gradual restrictions. “Using mathematical modelling, they postulated a strategy with the aim of achieving herd immunity by allowing the disease to run rampant through their population,” the authors explained.
“This strategy is like one achieved by a national vaccination programme to build ‘herd immunity’. The rationale behind this theory is by allowing ‘enough of citizens who are going to get mild illness to become immune’, a national disaster may be averted. “Unfortunately, this strategy failed due to the high complication rates, and the short incubation period and lethality of COVID-19. The initial UK strategy led to high rates of hospitalisation and intensive care unit admissions, straining their current health service capacity beyond breaking point.
“Using a mathematical stochastic transmission dynamic model to multiple publicly available datasets on cases in Wuhan and internationally exported cases from Wuhan, it was estimated that just by introducing travel restrictions, the reproductive number would decline from 2.35 to 1.05 within one week.” As a result of this data SA, like many countries around the world, introduced national lockdown, social distancing, and self-quarantine to control the spread of COVID-19 and flatten the curve. But with the SA economy nearing collapse, the authors questioned the sustainability of this strategy.
Most of the available reports to date indicate children infected with COVID-19 are less symptomatic. Furthermore, notable evidence indicates the burden of illness for COVID-19 lies predominantly in the patient age groups above 50 years, with case fatality rising sharply with each decade of life thereafter. Herein may lie a potential solution for SA.
“The median age of the SA population is 27.6 years with an average life expectancy of 64.8 years,” the authors said. “This implies we have a much younger population compared to countries like Spain, Italy and England who reported large numbers of COVID-19 related mortality. In SA, a hybrid model could be considered, wherein young children, adolescents, and adults under the age of 50 years, without any significant comorbidities, return to schools or universities, and employed adults return to [work].”
This would need to take place in a setting where precautionary measures of testing, surveillance, quarantine of infected individuals, social distancing, hygiene, and very close support of the elderly at-risk population continue. PROS “The potential benefit of targeting this approach is that the population under 50 years has the lowest case fatality rates for COVID-19.
Furthermore, easing the lockdown within this economically productive segment of the population will make a significant impact in mitigating the negative long-term financial impact of COVID-19 on our economy. “This phased approach may also help us to mitigate against the potential of the ‘re-emergence phenomenon’, where there is a sudden spike in the incidence of new COVID-19 cases.
The rationale of an approach of this nature would be for this young population of patients to acquire mild or asymptomatic disease with subsequent immune memory to COVID-19. This has the potential to disrupt the natural pattern of the spread of the illness within the population at large.
“A potential limitation to the implementation of this strategy is the unknown effect of COVID-19 on persons living with HIV and TB. However, there are preliminary reports that countries with the widespread use of the BCG vaccine seem to have a lower morbidity and mortality from COVID-19, thus potentially protecting our population.
“Unfortunately, the behaviour of SARSCoV-2 has been unlike any other infection we have previously been exposed to – and therefore there is no right or wrong answer. We can just postulate and hope for the best,” Professors Kalla and Abdullah concluded.
AUTHOR: Nicky Belseck, medical journalist