A baby's death could have been avoided if he had been admitted to hospital when his mother called an out-of-hours helpline, an inquest has heard.
William Mead died from septicaemia aged 12 months on 14 December.
Prof Peter Fleming said neither the NHS 111 service nor the out-of-hours GP had acted on a temperature change when his parents spoke to them on 13 December.
William's mother Melissa told the inquest in Cornwall he should not have died from something "so preventable".
'Not skilled professionals'
William had been suffering from a persistent cough when his parents called for help.
Expert witness Prof Fleming, from Bristol Children's Hospital, expressed concern that neither the 111 service nor the out-of-hours GP, Nicholas Walker, had acted on William's temperature which had been at 40C on 12 December but had fallen to 35C the next day.
He said: "One of the difficulties that 111 faces is that they are not talking to a skilled professional - they are working from a script, not their professional knowledge.
"The script does not cover what is a very rare event."
Prof Fleming said he was disappointed the "algorithm" used by the 111 service did not appear to have assessed the situation effectively.
Cornwall Coroner Dr Emma Carlyon asked Prof Fleming at the hearing in Truro if there was anything that could have been done that could have prevented the death.
He replied: "With the benefit of hindsight, had he been seen and admitted on the Saturday [13 December], I think there is a very good chance that his illness could have been treated successfully."
Prof Fleming said William died from a streptococcal infection and pneumonia leading to septicaemia. He said the infection had probably taken hold in the week leading up to William's death leading to a "rapid deterioration" on 12 and 13 December.
Dr Carlyon recorded a verdict of death by natural causes.
Speaking after the inquest Mrs Mead said she would like to see improvements in "the practice of all GPs and the 111 and out-of-hours services".
She said her son would be "missed beyond measure" and she and her husband had been "destroyed" by their loss.
South Western Ambulance Service NHS Foundation Trust, which provides the NHS 111 service in Cornwall, is yet to comment. Serco, which provided the out-of-hours GP service until 31 May 2015, said it would pass on any lessons learned to the new service providers.