The SHIVERS serosurvey

The purpose of the Southern Hemisphere Influenza and Vaccine Effectiveness, Research and Surveillance (SHIVERS) serosurvey in 2015 was to contribute to knowledge about influenza infection in the community and identify if participants developed immunity to influenza by the end of the winter and had influenza during the winter.

Study Overview

The study took place between February and November 2015 and involved about 1,500 adults and children randomly selected from general practices in Auckland.

After a short health survey, a blood sample was taken before the influenza season and, from May to September, weekly contact was used to check for cold or influenza symptoms. For those meeting the influenza-like illness case definition, and who hadn’t visited a GP, a nose or throat swab was taken to test for viruses or bacteria that cause influenza, colds or sore throats. At the end of winter, a longer questionnaire was completed and a second blood sample was collected. Detection of influenza RNA or antibody against haemagglutinin was used to provide information about the immunity that people in the community had against influenza and estimate influenza infection rates.

The results showed that 26% of people in the study were infected with influenza and four out of five of these people (80%) were asymptomatic carriers. These carriers could have spread the virus among their family, co-workers, classmates and patients without ever realising it. Children aged under 5 years and children aged 5–19 years were significantly more likely to contract influenza than adults aged 20–64 years. Pacific peoples had the highest risk of influenza compared with Maaori and European and other ethnic groups. People living in the same household as children were just over 1.5 times more likely to contract influenza than people who did not have children in their household.

When these results are applied to the New Zealand population in 2015

Around 1.1 million people (26%) would have been infected with influenza. Around 880,000 (80%) of these people were asymptomatic carriers who could have spread the virus among their family, co-workers, classmates and patients without ever realising it. Although most people with influenza symptoms would not have seen a doctor around 31,850 symptomatic people would have gone to see their GP and 2,209 were hospitalised.

References

  • Huang Q. Key findings - SHIVERS. 2016 New Zealand Influenza Symposium; Wellington, New Zealand; 2016.
  • Huang QS, Bandaranayake D, Wood T, Newbern EC, Seeds R, on behalf of the Southern Hemisphere Influenza Vaccine Effectiveness Research Surveillance Investigation Team. Risk factors and attack rates of seasonal influenza infection: Results of the Southern Hemisphere Influenza and Vaccine Effectiveness Research and Surveillance (SHIVERS) seroepidemiologic cohort study. J Infect Dis. 2018;219(3):347-57.