National surveillance for influenza and influenza-like illness in Vietnam, 2006−2010

Abstract

Influenza virus infections result in considerable morbidity and mortality both in the temperate and tropical world. Influenza surveillance over multiple years is important to determine the impact and epidemiology of influenza and to develop a national vaccine policy, especially in countries developing influenza vaccine manufacturing capacity, such as Vietnam. We conducted surveillance of influenza and influenza-like illness in Vietnam through the National Influenza Surveillance System during 2006–2010. At 15 sentinel sites, the first two patients presenting each weekday with influenza-like illness (ILI), defined as fever and cough and/or sore throat with illness onset within 3 days, were enrolled and throat specimens were collected and tested for influenza virus type and influenza A subtype by RT-PCR. De-identified demographic and provider reported subsequent hospitalization information was collected on each patient. Each site also collected information on the total number of patients with influenza-like illness evaluated per week. Of 29,804 enrolled patients presenting with influenza-like illness, 6516 (22%) were influenza positive. Of enrolled patients, 2737 (9.3%) were reported as subsequently hospitalized; of the 2737, 527 (19%) were influenza positive. Across all age groups with ILI, school-aged children had the highest percent of influenza infection (29%) and the highest percent of subsequent hospitalizations associated with influenza infection (28%). Influenza viruses co-circulated throughout most years in Vietnam during 2006–2010 and often reached peak levels multiple times during a year, when >20% of tests were influenza positive. Influenza is an important cause of all influenza-like illness and provider reported subsequent hospitalization among outpatients in Vietnam, especially among school-aged children. These findings may have important implications for influenza vaccine policy in Vietnam.

Surveillance of Severe Acute Respiratory Infection (SARI) for Hospitalized Patients in Northern Vietnam, 2011–2014

“…Vietnam has experienced large outbreaks of infection due to emerging respiratory viruses such as severe acute respiratory syndrome (SARS) in 2003, avian influenza A H5N1 (2005 and ongoing), and swine influenza A (H1N1) pdm09 (1,2). The rapidity with which these diseases can emerge and spread poses a serious threat to public health and socioeconomic growth and development, as well as highlights the need for strengthened disease surveillance and control.…”

“…Surveillance for severe acute respiratory infections (SARI) was established in hospitals in Hanoi following the SARS outbreak in 2003 and expanded in the north of Vietnam, after which sentinel hospitalized surveillance, a part of the National Influenza Surveillance System (NISS), began in 2005. NISS consists of a network of sentinel sites located in the 4 major regions (north, central, central highland, and south) of Vietnam (1). The 4 SARI sentinels were selected to include city hospitals (Hochiminh and Khanhhoa in central and southern Vietnam) and district provincial hospitals (Hoabinh and Langson in northern Vietnam).…”

“…Surveillance activities remain focused largely on influenza, with a particular emphasis on the early detection of zoonotic avian influenza viruses, A H5 and A H7N9 (1). However, the range of additional viral respiratory pathogens detected during routine surveillance has gradually expanded to comprise 13 viruses and subtypes.…”

Trivalent and quadrivalent influenza vaccination effectiveness in Australia and South Africa: results from a modelling study

“…The specific viral strain and lineage for each subtype are updated on an bi‐annual cycle (for the Northern and Southern Hemispheres) based on currently circulating strains 8. Since 2001, two distinct influenza B lineages (Yamagata and Victoria) have cocirculated, with one or both lineages causing a significant proportion of influenza infection in each year 9, 10, 11, 12, 13, 14, 15. In years when the predominant B lineage is incorrectly predicted, or where it is correctly predicted but there is a significant proportion of the other lineage, the TIV for that year leaves vaccinated individuals vulnerable to influenza infection from the ‘missing’ B lineage, since cross‐protection between B lineages is limited 16.…”

Non-annual seasonality of influenza-like illness in a tropical urban setting

“…Monthly data are normally too coarse to infer the presence of an annual transmission season or other periodic trends (if these exist) unless the time series is quite long. In fact, this is one of the reasons for disagreement in the current literature as some studies on respiratory disease in the tropics claim support for an annual transmission season 7,12,14,[26][27][28][33][34][35] while others show mixed or no evidence 8,13,31,[36][37][38][39][40] . Among these, some of the more weakly supported results are being used in public health policy to advocate for particular vaccination timings based on incorrectly identified seasonal signals 12,35 .…”