How to get both positive and negative number for x-axis in ggplot2 and rescale the y-axis in R?-CodePudding

I am drawing a graph using ggplot2 in R for two objects called A and B. My code is

  ggplot(test_error_bar_14_10_21, aes(x=levels, y=len, colour=index, group=index))   
  geom_errorbar(aes(ymin=len-ci, ymax=len ci), width=.03)  
  geom_line()  
  geom_point(size=3, shape=21, fill="white")   # 21 is filled circle
  xlab("Percentage(%population)")  
  ylab("Treatment on new cases")  
  scale_colour_hue(name="Type of indices",    # Legend label, use darker colors
                   breaks=c("doses/population", "death/population"),
                   labels=c("A", "B"),
                   l=40)                      # Use darker colors, lightness=40
  ggtitle("The Effect of different vaccines rates on \nA and B")  
  coord_flip()                                #rotate the graph (https://ggplot2.tidyverse.org/reference/coord_flip.html)
  expand_limits(y=0)                          # Expand y range
  scale_y_continuous(breaks=0:20*4)           # Set tick every 4
  theme_bw()  
  theme(legend.justification=c(1,0),
        legend.position=c(1,0))               # Position legend in bottom right

The result is

enter image description here

As can be seen, I have the negative results on x-axis, so what I should do to also mark the negative interval on x-axis ? I saw a post