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

It is important to note that during primary influenza infection, the innate and cellular responses play the key role in viral clearance whereas neutralizing antibodies are generated later and do not play a significant role unless the viral load is high/sustained [37] . The primary CTL response is detectable in blood after 6-14 days whereas the neutralizing antibody response peaks at four to six weeks [38] . Critically, the CTL response is downregulated after viral clearance [37] , disappears by day 21 post-infection [38] and is followed by a state of immunological 'memory' with antigen-specific T cells. The memory cells cannot prevent reinfection as well as specific antibodies could, but they can reduce the severity of the disease [37] . Together, these elements support the Win hypothesis: our parameter estimates indicate that the reinfection window occurred 17.8 days (s.d. 6.4 days) post-infection and lasted for 4.8 days (s.d. 4.8 days). This timing of susceptibility is in good agreement with the interval between the completion of CTL contraction and the full development of the neutralizing antibody response. Moreover, the reduced severity of most of the reinfection episodes in TdC ( §2) might be explained by the T-cell 'memory'.