You can use axes handle to update current plot, without plotting entire vector again. After plotting the first point using plot(), You can do something like this:
ax = gca; % get handle of current axes; line = get(ax, 'Children') % get handle to line object line.XData = [line.XData x_new]; line.YData = [line.YData y_new];
Here x_new and y_new are new data points you want to add to the plot. Remember to update XData and YData together otherwise, it may produce a warning.