Summary
DALYs due to Covid-19 in Malta were likely to have had the fourth largest population health impact relative to other diseases and injuries for 2020. The majority of the population health loss was due to mortality as it represented 95% of DALYs with 16 YLL per Covid-19 death. On comparing to the Scottish Covid-19 BoD study, our study’s mortality contributed to a lesser percentage to the DALYs than Scotland, where the latter reported mortality to contribute to 98% of DALYs [
22].
In our study, morbidity was driven mostly by post-acute consequences, followed by symptomatic community cases (moderate). Indeed, when maximizing both post-acute consequences and moderate cases, the estimated DALY exceeded the impact of Covid-19 from fourth to the second leading cause of disability in Malta. Therefore, although Covid-19 individuals that require hospitalisation, with or without intensive care support, have a considerable ill-health impact, the post-acute consequences, also called “long-haulers” might pose the largest cumulative impact on the population health, although this follows a degree of uncertainty. This finding corresponds with the Scottish Covid-19 DALYs estimate although different time periods were considered in this study [
23]. Nevertheless, it needs to be noted that following a comparison analyses between a Malta national burden of disease study for low back pain (LBP) to the GBD LBP estimates for Malta, it was concluded that the GBD overestimated the LPB burden [
24]. Hence, it is likely that the Covid-19 DALYs estimated in this study may place at a higher-ranking position than fourth leading cause of disability in Malta.
Strengths and weaknesses
The YLL calculation was based on the national reported cases (hospital, nursing homes and private residence deaths) that died while with Covid-19. Distinction was not made between those that died with Covid-19 or due to Covid-19. Since the onset of the pandemic, all deaths at hospital (even if initially negative for Covid-19), were tested for Covid-19 post-mortem however, deaths in private residents were not unless suspected by relatives that the deceased might have had Covid-19. This is more likely to have overestimated DALYs due to Covid-19, however this is counter-acted by the fact that deaths from early in the pandemic would have been less likely to have been identified as dying with Covid-19. The validity of the mortality estimate is furthermore supported by recent information on excess mortality. Compared to 2019, there have been 317 more deaths in 2020, which is in line with the number of reported Covid-19 deaths. Furthermore, caution needs to be put forward when comparing our study results to other Covid-19 burden of disease studies according to the mortality definition considered for the DALYs estimation.
The aspirational life table was used to calculate the YLL in order to facilitate comparative research considering that Covid-19 is a global issue, although acknowledge that this choice is an area of intense debate [
25].
All admissions to hospital were tested for Covid-19, with PCR testing repeated if any symptoms develop during the patient’s stay or the patient needed to undergo an invasive procedure. Hence, the Covid-19 pick up rate for in-patient cases was efficient. However, hospital data was only freely available on a weekly basis from August. Although assumptions had to be made for this time period, acute YLD is very small in relation to the YLL and so the impact of these assumptions will be minimal. However, one cannot dismiss the possibility that the assumptions might have led to overestimations or underestimations for some cases.
At a community level, a high swabbing rate has been implemented from the very start of the pandemic in Malta with contact tracing up to the second contact of an infected person [
3]. Therefore, Covid-19 positive cases, whether symptomatic or asymptomatic, were picked up at an early stage of the disease. Based on the literature it was assumed that the total Covid-19 population consisted of an additional 20% Covid-19 asymptomatic individuals that were never picked up [
13]. However, this was an estimated proportion originating from the literature and does not necessarily reflect the local undetected Malta cases, hence we cannot exclude the possibility of overestimations or underestimations of this asymptomatic cohort.
The disease model to calculate the health loss due to Covid-19 morbidity was based on the European Burden of Disease Network and ECDC consensus method, which was adopted for both prevalence- or pathogen- based YLD calculations [
9]. Meaning that any future presenting long-Covid conditions such as respiratory conditions, will be attributed to their relevant non-communicable diseases through prevalence data.
It needs to be noted that comorbidity data for the Covid-19 positive cases was not available. Common comorbidities such as diabetes and cardiovascular disease have been reported to increase the risk of acquiring Covid-19 infection (morbidity) as well as have a higher chance of mortality due to Covid-19 [
26,
27]. However, burden of disease studies, including the Global Burden of Disease (GBD) Study, perform adjustments to downscale YLD to correct for multimorbidity. Indeed, it is uncommon for the YLL to be adjusted in such cases [
28]. In terms of our study, since the major contribution to the DALYs was from the YLL rather than YLD, any adjustments to reduce the YLD would not have influenced our findings.
In our calculations, the post-acute consequences were based on assumptions since long Covid-19 remains largely uncertain and different entities provide different definitions and durations [
29,
30]. Indeed, the scenario analyses were performed to try out a number of different assumptions and scenarios, while evaluating the corresponding DALYs. However, since the YLD contributed to only 5% of the DALYs, fluctuations in post-acute consequences had a greater impact on DALYs only when maximizing the YLD health status outcome. It is recommended that further research is performed on post-acute consequences to have a better understanding on the progress of this condition.