The coronavirus disease 2019 (COVID-19) pandemic has spread to nearly every country in the world and caused over 5.5 million deaths.
After the initial emergence, many governments were forced to enact costly and restrictive measures to reduce the transmission of the disease, which lasted until the development of multiple different vaccines.
The mass administration of these vaccines allowed many to return to work, but new variants continued to emerge that showed worrying traits – such as increased transmission rates and the ability to evade both vaccine-induced and natural immunity.
The vaccine schemes have also been largely unequal and despite calls from scientists, many countries continue to provide their own citizens with booster jabs before providing vaccines to the developing world. Researchers from the University of London have been exploring the case-fatality rate of COVID-19 in thetop-vaccinated countries compared to the rest of the world.
The researchers’ data can be found on the medRxiv* preprint server.
The researchers gathered data from the World Health Organization (WHO) daily situation reports between 2020 and 2022. They chose a point 28 days after the first vaccine was approved and administered, as the cut-off for the post-vaccine period. To estimate cumulative daily reported case-fatality rate (rCFR) the scientists took the number of deaths per 100 confirmed COVID-19 cases.
Forecasting models, automatic time series forecasting models (ARIMA) and simple exponential smoothing (SES) were used to identify the global trend of rCFR, and Mann-Kendall trend analysis was used to identify the presence and direction of trends. A generalized linear mixed model with beta distribution was developed in order to identify any relationship between the rCFR and the explanatory variables. The time series models were used to forecast trends for each 10-day interval, while the SES was used as a benchmark for the performance of the ARIMA and prophet models. The performance of the time series models was analyzed and compared with more commonly used measures to evaluate the prediction significance. Predictor variables such as population density, GDP, percentage of individuals over 65, and prevalence of obesity were gathered from the World Bank and other UN sources.
The global reported CFR was estimated at 1.83 during January 2021 – and it has dropped by 35.5% to 1.18 by January 20222 (in the most vaccinated country). In the rest of the world, the rCFR in January 2021 was 2.32, and dropped to 2.2 by 2022 – a drop of only 8.4%. In Sub-Saharan Africa (SSA) the rCFR increased by 0.5%. The countries with the highest rCFR by January 2022 are Yemen (19.56%), Peru (8.75%), Mexico (7.44%), Sudan (7.07%), and Ecuador (6.09%). The correlating coefficient between vaccination rate and rCFR on Jan 2022 was estimated at -0.296.
The researchers present the estimated effect of each variable as relative risk (RR), with the significance shown by the p-value. They found that the COVID-19 vaccination, GDP and stringency index had been negatively associated with the COVID-19 rCFR indicating that the factors that contributed to the reduction of the rCFR were vaccination, GDP, and lockdown measures. The factor most positively associated with the COVID-19 CFR was the percentage of people aged over 65. Intraclass correlation coefficient was calculated by dividing the variance of the random effect by the total variance, showing a value of 0.634 – showing that the spatial unit effects account for 63.4% of total variance of weekly rCFR.
The ARIMA and Prophet model revealed that the rCFR of COVID-19 was declining. The ARIMA model performed better than both the Prophet and SES model, and showed a larger coefficient of determination with fewer errors. Both models forecast the ratio of COVID-19 rCFR will decrease significantly over the next 10 days.
The authors conclude that the global rCFR of COVID-19 has been steadily declining since May 2020 – despite the rate plateauing or even sometimes slightly increasing as new variants of concern emerge. This was most prevalent after the Delta variant become dominant. rCFR began declining when the mass vaccination programmes in developing countries started taking effect – as expected, it declined much quicker in these countries than in the rest of the world. The research the authors have undertaken could be of value to vaccine manufacturers and epidemiologists, and could potentially inform large-scale public health policies.
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.