The Dilemma of Influenza Vaccine Recommendations when Applied to the Tropics: The Brazilian Case Examined Under Alternative Scenarios

Abstract

Since 1999 the World Health Organization issues annually an additional influenza vaccine composition recommendation. This initiative aimed to extend to the Southern Hemisphere (SH) the benefits—previously enjoyed only by the Northern Hemisphere (NH)—of a vaccine recommendation issued as close as possible to the moment just before the onset of the influenza epidemic season. A short time between the issue of the recommendation and vaccine delivery is needed to maximize the chances of correct matching between putative circulating strains and one of the three strains present in the vaccine composition. Here we compare the effectiveness of the SH influenza vaccination adopted in Brazil with hypothetical alternative scenarios defined by different timings of vaccine delivery and/or composition. Scores were based on the temporal overlap between vaccine-induced protection and circulating strains. Viral data were obtained between 1999 and 2007 from constant surveillance and strain characterization in two Brazilian cities: Belém, located at the Equatorial region, and São Paulo, at the limit between the tropical and subtropical regions. Our results show that, among currently feasible options, the best strategy for Brazil would be to adopt the NH composition and timing, as in such case protection would increase from 30% to 65% (p<.01) if past data can be used as a prediction of the future. The influenza season starts in Brazil (and in the equator virtually ends) well before the SH winter, making the current delivery of the SH vaccination in April too late to be effective. Since Brazil encompasses a large area of the Southern Hemisphere, our results point to the possibility of these conclusions being similarly valid for other tropical regions.

Effectiveness of the Brazilian influenza vaccination policy, a systematic review

“…One study used both mortality and morbidity data 14 . Two others analyzed time series of laboratory-confirmed influenza cases to discuss seasonality 27,28 . Mortality studies have been used as outcomes to influenza-related death causes, which usually include influenza, pneumonia and obstructive respiratory diseases.…”

“…Viral subtypes that have circulated in Brazil show a similar match with both Northern and Southern hemisphere vaccine composition. According to the study, the use of the Southern hemisphere formulation earlier than currently scheduled (in January) or the use of the Northern hemisphere formulation would both increase the campaign's success 27 .…”

Influenza seasonality and vaccination timing in tropical and subtropical areas of southern and south-eastern Asia

“…lower temperatures and decreased humidity) may influence both viral transmission and host susceptibility. 3,32,33 Several countries, such as Bangladesh, Brazil, India and Viet Nam, have reported high influenza activity that coincides with rainy seasons, 15,16,19,25 while other countries, such as the Philippines, Singapore and Thailand, have reported semi-annual Influenza seasonality and vaccination timing in south-eastern Asia Siddhartha Saha et al…”

“…2).This is consistent with reports from Brazil stressing that the designation of influenza seasons by hemisphere may not apply to tropical and subtropical countries. 15 There is no ideal vaccine timing for equatorial countries with year-round influenza activity and without defined peaks of disease activity, such as Indonesia, Malaysia and Singapore. For these countries, the best recommendation would be to use the most recent vaccine formulation recommended by the World Health Organization (WHO) in that year.…”

“…13,14 Such undefined patterns of influenza activity further complicate vaccination recommendations and, in particular, the selection of an appropriate time for vaccination. 2,15 We undertook the analysis of influenza surveillance data from 10 countries in tropical and subtropical parts of southern and south-eastern Asia to characterize common trends in influenza circulation and therefore identify the most appropriate time for vaccination.…”