Explaining rapid reinfections in multiple-wave influenza outbreaks: Tristan da Cunha 1971 epidemic as a case study

Camacho, Anton; Ballesteros, Sébastien; Graham, Andrea L.; Carrat, Fabrice; Ratmann, Oliver; Cazelles, Bernard

TdC is a volcanic island in the South Atlantic Ocean. It has been inhabited since the nineteenth century and in 1971, the 284 islanders were living in the single village of the island: Edinburgh of the Seven Seas (figure 1b). Whereas the internal contacts were typical of close-knit village communities, contacts with the outside world were infrequent and mostly owing to fishing vessels that occasionally took passengers to or from the island. These ships were often the cause of introduction of new diseases into the population [14] . Focusing on influenza, several serological analyses between 1955 and 1963 provide important insights into the immune status of the adults among the 284 islanders present in 1971. Following an epidemic of A/H1N1 in 1954 during which most of the islanders were infected, antibodies to older influenza A and B types were detected in islanders over 20 years of age [15] . In 1961, when the volcano erupted, the island was evacuated to Britain and the islanders were given a polyvalent influenza vaccine that contained an A/H2N2 strain and a recent B strain. Serological studies showed a good response to this inoculation [16] . After the population returned to TdC in 1963, no influenza epidemic had been reported. In this context of a small population with a small and homogeneous immune repertoire against influenza virus, an unusual epidemic occurred in 1971, 3 years after the global emergence of the new subtype A/H3N2.