Study links shifts to buildup of susceptible hosts, explores similar shifts in heart-related deaths

A German analysis explores what underlies shifts in the timing of seasonal surges of respiratory diseases, as well as shifts in surges of heart-related deaths, that occurred after the COVID-19 pandemic began. Michael Sieber and Arne Traulsen of the Max Planck Institute for Evolutionary Biology, Germany, present these findings in the open-access journal PLOS Global Public Health on July 15, 2026.

Rates of respiratory infections such as the flu and RSV typically peak during seasons when transmission rates rise. Rates of death from any cause—not just from infection—follow a similar seasonal pattern.

However, the drivers underlying the exact timing of these surges have been unclear. The COVID-19 pandemic provided a unique opportunity to explore these dynamics, since interventions like social distancing and masking disrupted typical transmission patterns of other respiratory diseases. Sieber and Traulsen analyzed data on weekly respiratory infection rates and death rates in Germany, covering the last 14 years.

The analysis showed that, pre-pandemic, respiratory infections almost always surged for a few weeks in February and March. After the pandemic began, intervention efforts tamped down infections, eliminating one seasonal surge. Once infections rose again, surges shifted to December or earlier. Now, these peak weeks are gradually resuming pre-pandemic timing.

Using well-established epidemiological modeling tools, the researchers found that population-level loss of immunity after the skipped seasonal surge led to buildup of susceptible hosts, resulting in higher transmission earlier in the season. That is, seasonal transmission variations present a window of opportunity for a surge, and the size of the pool of susceptible hosts at the start of that window determines when, exactly, the surge occurs.

Similarly, typical seasonal surges in rates of death from any cause—but particularly from cardiovascular disease—also shifted earlier post-pandemic. Thus, respiratory infections may be key drivers of the timing of seasonal surges in cardiovascular deaths. More research is needed to explore this connection, but it aligns with other evidence that respiratory infections are a significant risk factor for cardiovascular disease.

On the basis of their findings, the researchers emphasize the importance of monitoring people’s infection history and improving vaccination coverage.

The authors add: “Respiratory infections are an important risk factor for cardiovascular problems” and that they were “surprised” to observe “seasonal dynamics of all-cause mortality” following respiratory infection timing patterns.

Journal: PLOS Global Public Health
DOI: 10.1371/journal.pgph.0006376
Publication Date: July 15, 2026

Source: EurekAlert