Use of amantadine in influenza: a second report.

Clinical influenza attacked 304 out of 576 boys at a west country boarding school. Influenza A/ENG/333/80 (H(1)N(1)), a drift from A/USSR/92/77, was isolated from 14 out of 40 throat swabs. Pre-epidemic sera from 64 new boys showed that 54 already had antibodies to H(1)N(1) and 40 of them had antibodies to this novel variant. Nevertheless, when their serum was re-examined post-epidemically, 36 showed a rise in antibody, indicating that infection had occurred.One hundred and twenty-six junior boys were given amantadine and, of these, 22 (17.4 per cent) developed influenza, whereas 218 (57 per cent) of 382 boys who did not take amantadine had influenza. The immune status was known for 64 boys, 43 of whom were given amantadine. Only five (11.6 per cent) became clinically ill while taking the drug, whereas 10 (47.6 per cent) of the remaining 21 boys became ill. When their serum was re-examined, it was found that 20/43 of those taking amantadine and 5/21 of those not taking the drug had subclinical infection. The two groups were comparable in their pre-epidemic antibody status and all lived within the same environment during the outbreak.It is concluded that amantadine secured a reduction in clinical influenza without protecting significantly against subclinical infection, thus allowing subtype specific immunity to develop.