A concentrated, immunoglobulin composition for treating subjects vaccinated against or infected with a pathogenic microorganism, is made by (a) selecting a population of individuals previously vaccinated against antigens associated with the pathogenic microorganism (b) identifying very high titer individuals by determining the level of specific antibodies immunoreactive with the pathogenic microorganism in the blood of the individuals (c) combining blood from the very high titer individuals and (d) purifying and/or concentrating the product of step (c). A concentrated immunoglobulin composition can include specific antibodies immunoreactive with a pathogenic microorganism, wherein the titer of specific antibodies is at least 5 times higher than the average titer of specific antibodies of a population of individuals previously vaccinated against antigens associated with the pathogenic microorganism. The composition has a relatively high protein concentration and a low percentage of protein aggregates. The pathogenic microorganism is preferably smallpox virus or vaccinia virus.
