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Clin Infect Dis. 2017 Nov 13;65(11):1905-1913. doi: 10.1093/cid/cix694.

Epidemiology and Relative Severity of Influenza Subtypes in Singapore in the Post-Pandemic Period from 2009 to 2010.

Author information

1
Saw Swee Hock School of Public Health, National University Health System, National University of Singapore.
2
Department of Infectious Diseases, Institute of Infectious Diseases and Epidemiology, Tan Tock Seng Hospital.
3
Department of Microbiology and Immunology, Yong Loo Lin School of Medicine, National University of Singapore.
4
World Health Organization (WHO) Collaborating Centre for Reference and Research on Influenza, VIDRL, Doherty Institute, University of Melbourne, Victoria, Australia.
5
Biodefence Centre, Singapore Armed Forces.
6
National Public Health Laboratory, Ministry of Health, Singapore, Singapore.
7
Department of Clinical Epidemiology, Institute of Infectious Diseases and Epidemiology, Tan Tock Seng Hospital.

Abstract

Background:

After 2009, pandemic influenza A(H1N1) [A(H1N1)pdm09] cocirculated with A(H3N2) and B in Singapore.

Methods:

A cohort of 760 participants contributed demographic data and up to 4 blood samples each from October 2009 to September 2010. We compared epidemiology of the 3 subtypes and investigated evidence for heterotypic immunity through multivariable logistic regression using a generalized estimating equation. To examine age-related differences in severity between subtypes, we used LOESS (locally weighted smoothing) plots of hospitalization to infection ratios and explored birth cohort effects referencing the pandemic years (1957; 1968).

Results:

Having more household members aged 5-19 years and frequent public transport use increased risk of infection, while preexisting antibodies against the same subtype (odds ratio [OR], 0.61; P = .002) and previous influenza infection against heterotypic infections (OR, 0.32; P = .045) were protective. A(H1N1)pdm09 severity peaked in those born around 1957, while A(H3N2) severity was least in the youngest individuals and increased until it surpassed A(H1N1)pdm09 in those born in 1952 or earlier. Further analysis showed that severity of A(H1N1)pdm09 was less than that for A(H3N2) in those born in 1956 or earlier (P = .021) and vice versa for those born in 1968 or later (P < .001), with no difference in those born between 1957 and 1967 (P = .632).

Conclusions:

Our findings suggest that childhood exposures had long-term impact on immune responses consistent with the theory of antigenic sin. This, plus observations on short-term cross-protection, have implications for vaccination and influenza epidemic and pandemic mitigation strategies.

KEYWORDS:

H1N1pdm09; birth cohort effect; cross-protection; seroepidemiology; severity

PMID:
29028950
PMCID:
PMC5850443
DOI:
10.1093/cid/cix694
[Indexed for MEDLINE]
Free PMC Article

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