Centenarians exposed to the Spanish flu in their early life better survived to COVID-19

Abstract

Background: Although it is known that mortality due to COVID-19 increases progressively with age, the probability of dying from this serious infection among the oldest-old population is little known, and controversial data are found in literature. Methods: We examine the mortality by year and month of birth of Belgians who had turned 100 during the current COVID-19 pandemic and whose birth fell on the years around the end the First World War and the outbreak of the H1N1 "Spanish flu" pandemic. Findings: The COVID-19 mortality of the "older" centenarians is significantly lower than that of "younger" centenarians, and this difference between the two groups reaches a maximum on August 1, 1918 as the discriminating cut-off date of birth. Having excluded the plausible impact of the end of WWI it becomes clear that this date corresponds to the time of reporting the first victims of the Spanish flu pandemic in Belgium. Interpretation: In this study, the striking temporal coincidence between the outbreak of the Spanish flu epidemic and the birth of the cohorts characterized by greater fragility towards COVID-19 in 2020 strongly suggests a link between exposure to 1918 H1N1 pandemic influenza and resistance towards 2020 SARS-Cov-2. It can be speculated that the lifetime persistence of cross-reactive immune mechanisms has enabled centenarians exposed to the Spanish flu to overcome the threat of COVID-19 a century later.

Centenarians born before 1919 are resistant to COVID-19

“…However, we observe that the younger centenarians display a strong excess of deaths while the older centenarians, born before 1919 (102 +) display the opposite, a deficit of deaths. The observation of this difference between younger and older centenarians is in agreement with data of Poulain et al [ 6 ].…”

“…The year of birth 1918 was, then, taken to separately analyse centenarians who died in 2020 [ 6 ], by dividing them in those dead at the age of 100 and 101 years, and in those dead at age of 102 + years. Both male and female 100–101 years old were extremely vulnerable to COVID-19.…”

“…According to the Belgian paper [ 6 ], there would be a link between exposure to the 1918 H1N1 pandemic influenza and resistance to SARS-Cov-2 in 2020. The Authors hypothesize that the persistence throughout life of cross-reactive immune mechanisms has allowed the centenarians exposed to the Spanish flu to overcome the threat of COVID-19 a century later [ 6 ], although, to best of our knowledge, it has never been proven the existence of this cross-reaction between influenza myxoviruses and coronaviruses, such as SARS-Cov-2. This does not rule out the role of Spanish flu in the reduced COVID-19 mortality of "older" centenarians.…”

“…Coronavirus disease 2019 (COVID-19), induced by SARS-CoV-2, may arise as a variety of clinical manifestations, ranging from an asymptomatic condition to a life-threatening disease associated with cytokine storm, multiorgan and respiratory failure [ 1 ]. Although mortality from COVID-19 progressively increases with age, there are controversial data in the literature on the probability of centenarians dying from this disease [ 2 – 6 ]. Anecdotal data suggest the resilience to COVID-19 of either centenarians, regardless of gender, or only male centenarians [ 2 , 3 ].…”

“…The centenarians, of both genders, born before August 1, 1918, showed a lower risk of excess mortality in 2020 in comparison to the mortality of previous years, when compared to centenarians born after August 1, 1918. The Authors pointed out that this date corresponds to the time when the first victims of the "Spanish flu" H1N1 pandemic in Belgium were reported [ 6 ].…”