Natality Decline and Miscarriages Associated With the 1918 Influenza Pandemic: The Scandinavian and United States Experiences

[tetano]

Oxford Journals
Medicine
Journal of Infectious Diseases
Volume204, Issue8
Pp. 1157-1164.

Natality Decline and Miscarriages Associated With the 1918 Influenza Pandemic: The Scandinavian and United States Experiences

Kimberly Bloom-Feshbach1,2,
Lone Simonsen1,3,
C?cile Viboud1,
K?re M?lbak4,
Mark A. Miller1,
Magnus Gottfredsson1,6 and
Viggo Andreasen1,5

1Division of International Epidemiology and Population Studies, Fogarty International Center, National Institutes of Health, Bethesda, Maryland
2Mount Sinai School of Medicine, New York, New York
3Department of Global Health, George Washington University, Washington, D.C
4Department of Epidemiology, Statens Serum Institut, Copenhagen, Denmark
5Department of Science, Systems, and Models, Roskilde University
6University of Iceland, Faculty of Medicine, Reykjavik, Iceland

Correspondence: Kimberly Bloom-Feshbach, BA, Fogarty International Center, National Institutes of Health, Building 16 (Stone House) - MSC 6705, Bethesda, MD 20892 (kimberlybf{at}gmail.com).

Abstract

(See the editorial commentary by Glezen, on pages 1151?3.)

Background. Although pregnancy is a recognized risk factor for severe influenza infection, the effect of influenza on miscarriages and births remains unclear. We examined the relationship between influenza and birth rates during the 1918 pandemic in the United States, Denmark, Sweden, and Norway.

Methods. We compiled monthly birth rates from 1911 through 1930 in 3 Scandinavian countries and the United States, identified periods of unusually low or high birth rates, and quantified births as ?missing? or ?in excess? of the normal expectation. Using monthly influenza data, we correlated the timing of peak pandemic exposure and depressions in birth rates, and identified pregnancy stages at risk of influenza-related miscarriage.

Results. Birth rates declined in all study populations in spring 1919 by a mean of 2.2 births per 1000 persons, representing a 5%?15% drop below baseline levels (P < .05). The 1919 natality depression reached its trough 6.1?6.8 months after the autumn pandemic peak, suggesting that missing births were attributable to excess first trimester miscarriages in ∼1 in 10 women who were pregnant during the peak of the pandemic. Pandemic-related mortality was insufficient to explain observed patterns.

Conclusions. The observed birth depressions were consistent with pandemic influenza causing first trimester miscarriages in ∼1 in 10 pregnant women. Causality is suggested by temporal synchrony across geographical areas.

http://jid.oxfordjournals.org/content/204/8/1157.short

 

[tetano]

Re: Natality Decline and Miscarriages Associated With the 1918 Influenza Pandemic: The Scandinavian and United States Experiences

Broadening Indications for Maternal Influenza Vaccination

W. Paul Glezen

Departments of Molecular Virology and Microbiology, and Pediatrics, Baylor College of Medicine, Houston, Texas

Correspondence: W. P. Glezen, MD, MVM Department, One Baylor Plaza, MS:BCM-280, Houston, TX, 77030 (wglezen{at}bcm.edu).

(See the article by Bloom-Feshbach et al, on pages 1157?64 .)

The primary indication for influenza vaccination of pregnant women is to decrease the risk of serious complications during pregnancy [ 1]. The case fatality rates for pregnant women during the influenza pandemics of 1918 and 1957 ranged from 20% to 50% in various reports [ 2]. As a consequence, pregnancy?with or without comorbidities?was considered a high-risk condition by the Surgeon General?s Advisory Committee. A large collaborative perinatal project sponsored by the National Institute for Neurological and Communicative Disorders and Stroke from 1959 to 1965 enrolled over 50 000 pregnant women and their offspring who were intensively followed for all events prior to and after delivery found that influenza vaccine administered to 2291 women during pregnancy had no untoward effects [ 3, 4]. From this study, it can be estimated that about 2 million women received influenza vaccine during pregnancy between 1959 and 1965. Despite the evidence of safety, influenza vaccine was no longer recommended for pregnant women without chronic underlying conditions after 1966 because ?influenza-associated excess mortality among pregnant women has not been documented except in the pandemics?? [ 5]. Reports of influenza-related deaths continued to occur, and the sensitivity of the data derived from death certificates was questioned [ 6, 7]. In the early 1990s, investigators looked at risk of influenza-associated hospitalizations during pregnancy and found significant excess occurrence of pneumonia that increased as the pregnancy progressed. This led to reconsideration of the indication for ?


http://jid.oxfordjournals.org/content/204/8/1151.short