Summary
Aqueous influenza vaccines seldom induce long-persistent protection against epidemic risk, and often fail to immunize up to one-third of the recipients, especially when there has been no previous immunological experience of the serotype of virus contained in the vaccine. Attempts to improve the situation by increasing the size or number of doses are limited by expense, toxicity and the time available in face of an oncoming epidemic. The future use of isolated viral antigens as vaccines may be limited by similar disadvantages.
Immunological adjuvants may make a valuable contribution in decreasing the minimum effective dose of antigen, thereby reducing the toxicity and expense of the vaccine, and increasing its availability. Adjuvant vaccines used in the past have been shown to induce higher mean titres of circulating virus-neutralizing or HI antibody in a higher proportion of the population than have aqueous vaccines, and the duration of immunity has been prolonged. The choice of adjuvants and the avoidance of untoward side-effects are discussed in this review.