Excess mortality during the COVID-19 pandemic was especially high among older persons and men

Peaks during COVID-19 waves

During the COVID-19 pandemic in 2020 and 2021, there was 0.34 percent excess mortality among Dutch people aged 65 and older, according to research by the LUMC. “That may seem like a small percentage, but it represents thousands of people,” say physician-researcher Eva Koster and biostatistician Liesbeth de Wreede of the LUMC’s Department of Biomedical Data Sciences.

This excess mortality was clearly linked to COVID-19 infections. “We saw peaks in mortality at times when the number of infections was high,” says Koster. Between COVID-19 waves, mortality was sometimes lower than expected. The risk of death was particularly high in the first month after infection and continued to be elevated compared to normal mortality rates in the months that followed.

Vaccination reduces the risk

After the vaccination campaign had begun in 2021, vaccinated people had a much lower risk of death after infection than unvaccinated people. This was true both shortly after infection and in the period that followed.

Among vaccinated people who were not infected, mortality was even temporarily slightly lower than expected. This is likely because people who get vaccinated are, on average, somewhat healthier. This is also known as the healthy vaccinee effect. Several factors play a role here. Koster explains: “People with a fever, for example, could temporarily not receive a vaccination. Socioeconomic differences also play a role.” This explains part of the lower mortality in the vaccinated group.

At the same time, the study shows that the healthy vaccinee effect accounts only in part for the difference in excess mortality after infection. “The protective effect of vaccination is clearly present,” Koster emphasizes. The researchers therefore conclude that vaccination played a major role in reducing excess mortality during the pandemic.

How did the researchers calculate this?

To investigate potential excess mortality, the researchers used an analysis model they developed themselves. This model utilizes data from Statistics Netherlands and follows individuals step by step over time: from healthy to infected, possibly to vaccination, and ultimately to death or survival. Such a model is called a multi-state model.

“The advantage is that you don’t just look at whether someone dies, but also at exactly when that happens and what precedes it,” says De Wreede. “This gives you better insight into how infection and vaccination are related to higher or lower mortality.”

Within this model, the researchers compared mortality during the pandemic with that of the preceding years, from 2015 through 2019. “We were able to calculate the normal expected mortality for every age group, for both men and women, for each day. By comparing mortality rates during the COVID-19 pandemic with expected mortality, we could calculate how many more people died than usual. That is what we call excess mortality,” says De Wreede.

The risk of excess mortality increases with age, especially among men

The older people were, the higher the excess mortality. The risk increased sharply, especially among the oldest age groups. There were also clear differences between men and women. In almost all age groups, men had a higher risk of excess mortality than women. This difference was not seen in the youngest group. The highest risk of excess mortality was observed among men aged 90 and older.

“The risks increase significantly with age,” says Koster. “The results show that age and sex played an important role in the risk of excess mortality during the COVID-19 pandemic and that it made sense to prioritize older adults for vaccination.”

What does this mean for the future?

The study shows that the risk of excess mortality during the COVID-19 pandemic depended not only on infection but also on age and gender. The model also shows that vaccinations prevented a significant amount of excess mortality. At the same time, not all infections and vaccinations were included in the analysis, for example because not everyone got tested or gave consent to share vaccination data.

According to Koster and De Wreede, these insights are also relevant for future pandemics. “With models like this, we can identify who is at risk more quickly and assess the impact of vaccinations,” they say. “This helps to make better decisions, such as determining who should be vaccinated first. By prioritizing vulnerable groups, such as older persons, a substantial amount of excess mortality can be prevented in a future pandemic.”

Further information

The study on excess mortality has recently been published in the European Journal of Epidemiology and was established through a collaboration between the departments of Biomedical Data Sciences, Clinical Epidemiology, and the Leiden University Center for Infectious Diseases (LUCID) at LUMC. The study was part of the subprogram “Excess Mortality in the Netherlands 2020–2021” of ZonMw’s COVID-19 program. In this program ZonMw funded and supported various research groups to conduct independent research into the reasons and causes of excess mortality in the Netherlands (https://www.zonmw.nl/en/research-reasons-and-causes-excess-mortality-during-covid-19-pandemic).