  Assume that $G$ is a graph with cover ideal $J(G)$. For every integer $k\geq
1$, we denote the $k$-th symbolic power of $J(G)$ by $J(G)^{(k)}$. We provide a
sharp upper bound for the regularity of $J(G)^{(k)}$ in terms of the star
packing number of $G$. Also, for any integer $k\geq 2$, we study the difference
between ${\rm reg}(J(G)^{(k)})$ and ${\rm reg}(J(G)^{(k-2)})$. As a
consequence, we compute the regularity of $J(G)^{(k)}$ when $G$ is a doubly
Cohen-Macaulay graph. Furthermore, we determine ${\rm reg}(J(G)^{(k)})$ if $G$
is either a Cameron-Walker graph or a claw-free graph which has no cycle of
length other that $3$ and $5$.
