The 3rd quarter figures are the first of the Spanish Flu peaks. A careful look does show that the 1918 numbers were higher for the 10 to 39 age group but not by enough to have worried the authorities.
In Benfleet we had one case we can account for who is Private William James Ernest Revell. On 24th September 1918 he was home on leave, but died only four days later on the 28th September in a hospital in France from double pneumonia aged 23. He is recorded on the Benfleet War Memorial.