Reviewing a rich set of studies from history, biology, and the social sciences published from 1918 to date, Aligne (p. 1454) concludes that extreme congestion created by the First World War is one “essential cause” of the high lethality during the 1918 influenza in military camps, trenches, and especially among soldiers on troopships. The author claims that this conclusion holds well even after discussing several arguments against the role of virulence enhancement during extreme overcrowding.
EXTREME DISEASE BURDEN ON ACTIVE FLEETS
Two particularly relevant studies that cast light on the extreme overcrowding hypothesis were not included in the review by Aligne.1,2 These studies deal with the Brazilian and New Zealand fleets, both active during the war. The average mortality rate among eight ships in the Brazilian fleet was especially high at 8.2%, with even up to 13% to 14% mortality on two of the ships. Mortality on the New Zealand troopships was lower, but morbidity was extremely high at 90%.2 Both articles proposed explanations for the high mortality, including the crew’s lack of immunity (due to less exposure to H1-like viruses before 1918 or during the first wave) and the typical young age of the crew, which was among the most vulnerable young adult age groups globally (ages 20–40 years). However, the close living conditions, poor ventilation, and a high number of people gathered in enclosed spaces were also possible causes of the high mortality rates.
NEW RESEARCH ON NAVY RECRUITS IN A NEUTRAL COUNTRY
A recently written thesis by the first author of this editorial3 is an important contribution to the literature because it uses high-level qualitative and quantitative archival data about soldiers in the Norwegian navy, which remained neutral during the war. The data show that one naval training ship, Kong Sverre, which was stationed along the coast of the city of Horten with 517 soldiers on board, had a morbidity rate in the fall of 1918 of 31%, with 46% of the cases developing pneumonia and requiring hospitalization. Mortality was 8.1%, and lethality was 27%, which were more than 10 times higher than in similar, presumably healthy male age groups among Norwegian civilians.
Mortality and lethality for the generally healthy young soldiers on Kong Sverre (8.1% and 27%) was even higher than 1918 influenza fall mortality and lethality among persons with serious comorbidities, such as patients at six Norwegian psychiatric asylums (2.3% and 9.8%) and two Norwegian tuberculosis sanatoriums (0.74% and 17.8%).4,5 Although there were nine other vessels in the Norwegian navy, no ships were as large (in terms of size and number of soldiers on board) and as crowded as Kong Sverre, and mortality rates in the other ships were on par with what was seen among presumably healthy males of the same age in average civilian settings. Torjussen concluded that extreme overcrowding was the main reason that so many contracted severe disease and died on Kong Sverre, a ship that was nicknamed locally “The Ship of Death” and had one of the highest mortality rates of any ships internationally during the 1918 influenza pandemic.3
We agree with Aligne that extreme crowding is a major risk factor for severe disease enhancement during the 1918 influenza pandemic and that avoiding such a setting is key to reducing extreme mortality and lethality during pandemics.
ACKNOWLEDGMENTS
We received funding from the Research Council of Norway as part of the project “PANRISK: Socioeconomic risk groups, vaccination and pandemic influenza” under grant agreement 302336.
CONFLICTS OF INTEREST
The authors have no conflicts of interest to declare.
Footnotes
See also Aligne, p. 1454.
REFERENCES
- 1.Schuck-Paim C, Shanks GD, Almeida FEA, Alonso WJ. Exceptionally high mortality rate of the 1918 influenza pandemic in the Brazilian naval fleet. Influenza Other Respir Viruses. 2013;7(1):27–34. doi: 10.1111/j.1750-2659.2012.00341.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2.Summers JA, Wilson N, Baker MG, Shanks GD. Mortality risk factors for pandemic influenza on New Zealand troop ship, 1918. Emerg Infect Dis. 2010;16(12):1931–1937. doi: 10.3201/eid1612.100429. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 3.Torjussen C. «Dødsseileren» - losjiskipet i Horten. En kvalitativ og kvantitativ analyse av årsakene til den høye dødeligheten på MS «Kong Sverre» under spanskesyken i 1918. Borre, Norway: Universitetet i Sør-Øst Norge; 2022. [Google Scholar]
- 4.Mamelund S-E, Dimka J. Tuberculosis as a Risk factor for 1918 influenza pandemic outcomes. Trop Med Infect Dis. 2019;4(2):74. doi: 10.3390/tropicalmed4020074. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 5.Dimka J, Mamelund S-E. 1918 Influenza outcomes among institutionalized Norwegian populations: implications for disability-inclusive pandemic preparedness. Scand J Disabil Res. 2020;22(1):175–186. doi: 10.16993/sjdr.725. [DOI] [Google Scholar]