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The authors reply:

Published online by Cambridge University Press:  02 August 2016

S. G. SULLIVAN  and
B. J. COWLING
S. G. SULLIVAN*
Affiliation:
WHO Collaborating Centre for Reference and Research on Influenza, Melbourne, Australia Fielding School of Public Health, University of California, Los Angeles, CA, USA
B. J. COWLING
Affiliation:
WHO Collaborating Centre for Infectious Disease Epidemiology and Control, School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong Special Administrative Region, China
*
(Email: [email protected])
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Abstract

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Type
Correspondence
Information
Epidemiology & Infection , Volume 144 , Issue 12 , September 2016 , pp. 2690
Copyright
Copyright © Cambridge University Press 2016 

We thank Nauta [Reference Nauta1] for providing further explanation on the need to control calendar time in TNDs. We agree that such adjustment is probably redundant in temperate climates with well-defined influenza seasons and well-defined influenza vaccination campaigns. However, we caution those researchers conducting TND studies in tropical and sub-tropical regions where there may be multiple influenza seasons. A vaccination campaign scheduled for April or September, when the Southern and Northern hemisphere vaccines are typically available, may fall before, during or even after the peak of the influenza season. When the campaign and influenza season coincide, vaccination status would not be in steady state and the need to adjust for calendar time persists.

References

1.Nauta, JJP. Adjusting for calendar time in a TND influenza study [Letter]. Epidemiology and Infection. doi:10.1017/S0950268816000832.Google Scholar