You just want to connect the paired samples, as in a bi-partite plot? I think that these plots have a different name each time one asks a different person.

This code worked for me. Note that I had to melt the data-frame first such that the paired observations were in a single column:

#melt dataframe
mydf<- melt(mydf, id.vars="sampleID", variable.name="vitD", value.name="value")

#plotting in ggplot2
graph <- ggplot(data=mydf, aes(x=vitD, y=value, group=sampleID)) +

    geom_line(size=0.3) +

    geom_point(size=2.5, shape=21, fill=colour, colour='black') +

    xlab("") + ylab("Vitamin D (ng/ml)") +

    ylim(0, 100) +

    #Modify various aspects of the plot text and legend
    theme(
        legend.position="none",
        legend.background=element_rect(),
        plot.title=element_text(angle=0, size=10, face="bold", vjust=1),

        axis.text.x=element_text(angle=0, size=10, face="bold", vjust=0.5),
        axis.text.y=element_text(angle=0, size=10, vjust=0.5),
        axis.title=element_text(size=10),

        #Legend
        legend.key=element_blank(),     #removes the border
        legend.key.size=unit(1, "cm"),      #Sets overall area/size of the legend
        legend.text=element_text(size=8),   #Text size
        title=element_text(size=8)) +       #Title text size

    ggtitle(title) +

    geom_hline(yintercept=30, colour="red", size=1.25, linetype="solid")