Reversed passive haemagglutination-inhibition method for the estimation of antivaccinia antibodies.

A reversed passive haemagglutination-inhibition (HAI) method has been evolved for measuring antivaccinia antibodies. Tanned sheep erythrocytes were sensitized with a bovine hyperimmune antivaccinia γ-globulin solution. The sensitized erythrocytes were agglutinated by a purified suspension of vaccinia virus. Haemagglutination was inhibited by sera containing antivaccinia antibodies and so the antivaccinia titres could be measured. Reversed passive HAI titres were compared with Hirst-type HAI, complement-fixing and neutralization titres in sera of persons vaccinated for the first time and also in persons revaccinated. A correlation was found between the reversed passive HAI titres and the neutralization titres.