Intense seasonal A/H1N1 influenza in Mexico, winter 2013-2014

Javier Dávila-Torres, Gerardo Chowell, Víctor H. Borja-Aburto, Cécile Viboud, Concepción Grajalez-Muñiz, Mark A. Miller

Research output: Contribution to journalArticlepeer-review

13 Scopus citations

Abstract

Background and Aims: A recrudescent wave of pandemic influenza A/H1N1 affected Mexico during the winter of 2013-2014 following a mild 2012-2013 A/H3N2 influenza season. Methods: We compared the demographic and geographic characteristics of hospitalizations and inpatient deaths for severe acute respiratory infection (SARI) and laboratory-confirmed influenza during the 2013-2014 influenza season compared to previous influenza seasons, based on a large prospective surveillance system maintained by the Mexican Social Security health care system. Results: A total of 14,236 SARI hospitalizations and 1,163 inpatient deaths (8.2%) were reported between October 1, 2013 and March 31, 2014. Rates of laboratory-confirmed A/H1N1 hospitalizations and deaths were significantly higher among individuals aged 30-59years and lower among younger age groups for the 2013-2014 A/H1N1 season compared to the previous A/H1N1 season in 2011-2012 (χ2 test, p<0.001). The reproduction number for the winter 2013-2014 influenza season in central Mexico was estimated at 1.3-1.4, in line with that reported for the 2011-2012 A/H1N1 season but lower than during the initial waves of pandemic A/H1N1 activity in2009. Conclusions: We documented a substantial increase in the number of A/H1N1-related hospitalizations and deaths during the period from October 2013-March 2014 in Mexico and a proportionate shift of severe disease to middle-aged adults, relative to the preceding A/H1N1 2011-2012 season. In the absence of clear antigenic drift in globally circulating A/H1N1 viruses in the post-2009 pandemic period, the gradual change in the age distribution of A/H1N1 infections observed in Mexico suggests a slow build-up of immunity among younger populations, reminiscent of the age profile of past pandemics.

Original languageEnglish (US)
Pages (from-to)63-70
Number of pages8
JournalArchives of Medical Research
Volume46
Issue number1
DOIs
StatePublished - 2015

Keywords

  • A/H1N1 influenza pandemic
  • Age distribution
  • Drift
  • Immunity
  • Influenza vaccine
  • Transmissibility

ASJC Scopus subject areas

  • Medicine(all)

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