A Sydney paediatrician has called on the NRL to rein in its footballers and their partners over spreading anti-vax misinformation in a letter that has been signed by at least 300 other doctors.

Dr Claire Egbert has written to the NRL executive and the Gold Coast Titans club in the wake of social media posts by Shanelle Cartwright, the wife of Titan’s player Bryce Cartwright, promoting anti-vaccination messages.

Earlier this week, Ms Cartwright, soon to have her second baby, revealed through a Q&A on her Instagram account that she was not going to vaccinate either of her two children.

Since then, Ms Cartwright has continued to post comments and messages — to her more than 7600 followers — supporting her stance.