Cookies on this website

We use cookies to ensure that we give you the best experience on our website. If you click 'Accept all cookies' we'll assume that you are happy to receive all cookies and you won't see this message again. If you click 'Reject all non-essential cookies' only necessary cookies providing core functionality such as security, network management, and accessibility will be enabled. Click 'Find out more' for information on how to change your cookie settings.

BACKGROUND:The extent to which influenza recurrence depends upon waning immunity from prior-infection is undefined. We used antibody titres of Ha-Nam cohort participants to estimate protection curves and decay trajectories. METHODS:270 households participated in influenza-like-illness surveillance and provided blood at intervals spanning RTPCR-confirmed transmission. Sera were tested in haemagglutination inhibition assay. Infection was defined as RTPCR+ influenza-like-illness and/or seroconversion. Median protective titres were estimated using scaled-logistic-regression to model pre-transmission titre against infection status in that season, limiting analysis to households with infection(s). Titres were modelled against month since infection using mixed-effects linear regression to estimate decay and when titres fell below protection-thresholds. RESULTS:295 and 314 participants were infected with H1N1pdm09-like and A/Perth/16/09-like (H3N2Pe09) viruses, respectively between December 2008-2012. The proportion of householders not-infected (protected) rose more steeply with titre for H1N1pdm09 than for H3N2Pe09, and estimated 50% protection titres were 19.6 and 37.3, respectively. Post-infection titres started higher against H3N2Pe09 but decayed more steeply than against H1N1pdm09. Sero-protection was estimated to be sustained against H1N1pdm09 but to wane by 8-months for H3N2Pe09. CONCLUSIONS:Estimates indicate that infection induces durable sero-protection against H1N1pdm09 but not H3N2Pe09, which could in part account for the younger age of A(H1N1) versus A(H3N2) cases.

Original publication




Journal article


The Journal of infectious diseases

Publication Date



Oxford University Clinical Research Unit and Wellcome Trust Major Overseas Programme, Hanoi, Viet Nam.