Mortality and Excess Mortality: Improving FluMOMO

FluMOMO is a universal formula to forecast mortality in 27 European countries and was developed on EuroMOMO context, www.euromomo.eu. The model has a trigonometric baseline and considers any upwards deviation from that to come from flu or extreme temperatures. To measure it, the model considers two variables: influenza activity and extreme temperatures. With the former the model gives the number of deaths because of flu and with the latter the number of deaths because of extreme temperatures.In this article we show that FluMOMO lacks important variables to be an accurate measure of, all causes mortality and flu mortality. Indeed, we found, as expected, that population ageing and exposure to the risk of death can’t be excluded from the linear predictor.We also show that FluMOMO assumes independent errors, but errors produced by the model are not independent. To overcome that we model weekly deaths as an autoregressive process (lag of one week), which improved the results. This step also allowed us to finish with FluMOMO trigonometric baseline and have a better fit to weekly deaths through demographic, meteorological and health variables together with lagged number of deaths.The model used data from Portugal between 2009 and 2020, on ISO-week basis. We used Negative Binomial generalized linear models to estimate the weekly number of deaths as an alternative to traditional overdispersion Poisson. As explanatory variables found to be statistically significant, we registered: the number of deaths from previous’ week, the influenza activity index, the population average age, the heat waves, the flu season, the number of deaths with COVID-19 and the population exposed to the risk of dying.Considering as excess mortality the number of deaths above the best estimate of deaths from our model, we concluded that 2020 excess mortality (net of, COVID-19 deaths, heat wave of July and ageing) is low or inexistent.The model also allows us to have the number of deaths arising from flu and we conclude that FluMOMO is overestimating deaths from flu on 78%. Averages from probability of dying are obtained as well as the probability of dying from flu. The latter is shown to be decreasing over time, probably due to the increase of flu vaccination. Higher mortality detected with COVID-19 start, in March-April 2020, was probably from COVID-19 deaths not recognized as such.