Epidemiological study of neutralizing antibodies in the general population in China.

a<p>The titers (vaccinia-neutralizing activity) were determined using the neutralization assay described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0033392#pone-0033392-t001" target="_blank">Table 1</a>. Arbitrary intervals were established as a qualitative reference for the potency of a determined serum, i.e., negative (<30), low (30–100), and high (>100).</p>b<p>the percentage of positive VTT NAbs increased with age.