Correcting under-reported COVID-19 case numbers

Alexander Lachmann

Overlapping the reported exponential decrease from China, Italy, and Iran show a reproducible growth rate decline (Figure 2) . We estimate the growth rate spline parameters a and b for EDG(t) with a = 0.4169 and b = 0.07073. This suggests that the growth rate after nationwide lockdown halves about every 10 days. By applying the proposed correction, the number of adjusted cases is significantly higher for most countries. Figure 3a shows the population age distribution of the US, Italy, and China compared to South Korea. Figure 3b shows the expected number of fatal outcomes for a 100% infection rate. The vulnerability factor for the US compared to South Korea is 1.07. This means that the population is equally vulnerable to fatal outcomes of COVID-19 infections. Italy, in contrast, has a vulnerability factor of 1.57. This is due to a higher fraction of the population being at a higher risk of death. This would indicate the expected CFR would be 57% higher in Italy compared to South Korea. China, with a younger population relative to South Korea, has a vulnerability factor of 0.63. The expected CFR in China should be lower than in South Korea based on the population risk. After applying the case adjustment, we observe a significant increase in the number of COVID-19 infections. The discrepancy in reported CFRs in combination with favorable population scores in the case of China and Iran suggest a over-proportional number of unreported COVID-19 infections. Figure 4 shows the projections of cumulative deaths for eight countries. The US has a projected number of COVID-19 fatalities of more than 80,000 before growth is reduced and new deaths are rare. The hospitalization per day will increase exponentially and reach its maximum in 12 to 14 days from the time of writing. Similar dynamics can be observed for other European countries. Table 2 shows the predicted number of cases and the Vulnerability Factor for seven countries. It suggests current infections in the US and Spain have exceeded 1.4 million.