Dependence on the birth season of the antibody level against West Nile virus in the Pakistani population.

Variation of antibody level against West Nile (WN) virus depending on the season of birth was followed among 151 paired serum samples of healthy Pakistani persons in Karachi, collected twice in July and October, 1985. The persons born during the months between February and June had lower positive antibody rate and lower responsiveness in haemagglutination inhibition and neutralizing tests against WN virus than those born during the other months. This phenomenon implies that the ability to produce antibodies against WN virus among Pakistani persons may depend on their birth season.