Background. The (H1N1)pdm09 live attenuated influenza vaccine (LAIV) strain was changed for the 2017-2018 influenza season to improve viral fitness, following poor protection against (H1N1)pdm09 viruses in 2015-2016. We conducted LAIV virus shedding studies to assess the effect of this change. Methods. Children aged 2-18 years were recruited to receive LAIV in the 2016-2017 (n = 641) and 2017-2018 (n = 362) influenza seasons. Viruses from nasal swabs taken 1, 3, and 6 days postvaccination were quantified by reverse-transcription polymerase chain reaction and area under the curve titers were determined. Presence and quantity of shedding were compared between strains and seasons with adjustment for age and prior LAIV (n = 436), inactivated seasonal vaccine (n = 100), or (H1N1)pdm09 vaccine (n = 166) receipt. Results. (H1N1)pdm09 detection (positivity) in 2016-2017 and 2017-2018 (11.2% and 3.9%, respectively) was lower than that of H3N2 (19.7% and 18.7%, respectively) and B/Victoria (28.9% and 33.9%, respectively). (H1N1)pdm09 positivity was higher in 2016-2017 than 2017-2018 (P =.005), but within shedding-positive participants, the (H1N1)pdm09 titer increased in 2017-2018 (P =.02). H3N2 and influenza B titers were similar between seasons. Positivity declined with age, and prior vaccination reduced the likelihood of shedding influenza B but not (H1N1)pdm09. Conclusions. The (H1N1)pdm09 titer increased in 2017-2018, indicating more efficient virus replication in shedding-positive children than the 2016-2017 strain, although overall positivity was reduced. Age and vaccination history require consideration when correlating virus shedding and protection.
Bibliographical noteFunding Information:
Financial support. This work was supported by the NIHR Policy Research Programme (National Vaccine Evaluation Consortium, grant number 039/0031, holder E. M.).
Acknowledgments. The four live attenuated influenza viruses were kindly provided by Helen Bright (MedImmune). The authors thank Angie Lackenby, Monica Galiano, Janice Baldevarona, Jade Cogdale, Tiina Talts, Piotr Patrzylas, Praveen Sebastianpillai, and Olivia Box Power for technical support and data management at the Respiratory Virus Unit, National Infection Service, Public Health England (PHE) Colindale. The Safety of nasal influenza immunisation in children with asthma-4 (SNIFFLE-4) Study investigators are Alexandra Adams, Mich Erlewyn-Lajeunesse, Katy Fiddler, Louise Fleming, Atul Gupta, Heather Hanna, Stephen Hughes, Andrew Ives, Nicola Jay, Sonal Kansra, Sam Moss, Clare Murray, Prasad Nagakumar, Hitesh Pandya, Satish Rao, Graham Roberts, Sejal Saglani, Paul Seddon, Ian Sinha, Gary Stiefel, Huw Thomas, and Paul Turner. The authors thank the vaccine research nurses in Hertfordshire and Gloucestershire for recruitment and follow-up of the study participants and data management, and staff in the Immunisation Department for study administration and data entry. The authors acknowledge the support of the National Institute for Health Research (NIHR) Health Protection Research Unit in Respiratory Infections at Imperial College London in partnership with PHE.
Potential conflicts of interest. P. J. T. has received grants from the UK Medical Research Council. All other authors report no potential conflicts of interest. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed.
- Vaccine effectiveness
- Virus shedding