Kinetics of the antibody response in pigs against PRRSV-JA142 infection. A The PRRSV-specific antibody titre in pigs was measured by ELISA. The dashed line indicates the designated threshold value (S/P ratio of 0.4). B Weekly serum virus-neutralizing (SVN) antibody titres in uninfected (NC) and infected pigs obtained using homologous virus as the recall antigen. The bars represent the means, and the error bars represent the standard errors of the mean (SEM).