The disease burden of Long COVID presents an immense
public health challenge.
public health challenge.
COVID-19 and Long COVID
Coronavirus disease 2019 (COVID-19) was officially declared a worldwide pandemic by the World Health Organisation (WHO) in March 2020.
Since then, great efforts have been made to curb the spread of the virus and COVID-19, chiefly through increasing vaccination as a preventative measure to reduce transmission, disease severity and mortality. While these efforts are ongoing, a growing number of observational, post-infection studies now recognise another pressing issue – the long-term, chronic effects of COVID-19 following recovery from acute illness.
Dubbed ‘post-COVID-19 syndrome’, or ‘Long-COVID’, the condition is characterised by the experience of lingering and/or newly-developed symptoms (sequelae) over a minimum of 12 weeks (≥12 weeks) following resolution of initial COVID-19 infection. To date, considerable numbers of patients have reported grappling with Long-COVID, frequently over a protracted period of 6 to 12 months or more.
Long COVID Statistics
While estimates vary, many studies suggest that upwards of 20-35% of people diagnosed with COVID-19 will continue to experience at least one post-infection symptom over the long-term, with this number rising even further among those hospitalised for severe COVID-19.
According to the United Kingdom Office for National Statistics, roughly 3% of the population has self-reported experiencing symptoms of Long-COVID as of 7 July 2022. This shows an upward trend from 1 Aug 2021 (where ~1.5% of the population had originally self-reported experiencing symptoms of Long-COVID).
Long COVID’s Burden of Disease
Somewhat worryingly, Long-COVID does not appear to be limited to the infirm but also commonly affects younger, fitter and previously-healthy individuals, many of whom suffered only mild illness in the first instance.
Precise diagnosis of Long COVID has proven difficult for many healthcare providers owing to complex symptomology and a lack of sufficient knowledge of the disease amongst the medical community. While awareness and concern surrounding Long COVID has steadily grown two years into the pandemic, a preponderance of focus has been dedicated to cataloguing subtleties of active COVID-19 infection in lieu of long-term effects and complications outside of the immediate window of infectivity. It is therefore very likely that statistics for Long COVID have been underrepresented, as many studies report widely differing estimates of Long COVID prevalence in observed survivor populations.
Long-COVID presents an immense, multi-faceted public health burden that must be understood in terms of the multitude of physiological, psychological, social, financial and functional consequences it incurs. These can hamper individuals’ abilities to manage day-to-day activities to a sufficient standard and impair workplace productivity and performance, financial stability, inter-personal relationships, physical abilities, mental health, and more. Secondary implications on industry, GDP, healthcare systems, and national and global economy are hugely significant.
To date, there is no successful treatment for management of Long COVID.
The link between acute COVID-19 infection, Long COVID, and telomere length
A strong, effective immune response and lasting immune memory relies on ample expression of T and B lymphocytes.
Lymphopenia is a phenomenon characterised by exhaustion of circulating T and B cells, wherein inability to restore depleted T-cells can severely compromise convalescence and long-term immune function. While this effect has transiently been observed across many acute viral respiratory infections, the extent to which this occurs in acute COVID-19 infection may be predictive of disease progression and severity.
One of the key mediators of T-cell clonal expansion capacity is telomere length. Telomere attrition increases with age and disease, and also appears to correlate with severity of COVID-19. This may in part account for increased COVID-19 mortality with age. Younger individuals with innately shorter telomere length may also be at greater risk of severe COVID-19 and mortality.
Short T-cell telomere length may therefore hamper both recovery from acute COVID-19 infection, as well as long-term adaptive immunity against COVID-19 due to limited capacity for proliferation of memory T-cells, regardless of the method of immune priming (i.e. natural infection versus vaccination).
To-date, the precise mechanisms behind Long COVID continue to be explored. However, multiple theories surrounding contributing factors have been proposed, including accumulated tissue damage following acute infection, lingering chronic inflammation [due to insufficient viral clearance], and resurgence of other old, dormant viruses further exacerbating disease symptoms. Addressing the ability of the immune system to appropriately deal with these underlying issues may be paramount to resolving persistent symptoms of Long COVID.
While recent reports indicate vaccinated individuals appear less likely to develop Long COVID following acute infection than those who are unvaccinated, prevalence of Long COVID in both groups still represents a significant healthcare burden – one that will likely continue to require address over the long-term. Furthermore, although greater severity of COVID-19 infection increases likelihood of Long COVID in survivors, mild or asymptomatic infection does not appear to preclude development of Long COVID.
