Check with your doctor because flu shots are changed from year to year depending on the variety which is going around. There is also a specific time period for which they last the best and for those who are older, it seems that we lose the effects of it faster. That's why the CDC recommends a kind of a double-dose variety for the older and a few others - like people who are very much overweight because they too lose the effect faster.
Flu vaccines come out about September of each year and the flu season usually last between October - March; about 6-months+/-. So just make sure with your Doctor or Pharmacist where you get this immunization that you are still going to be protected since you got it in July. That sounds to me like you may have gotten last years version. You need current protection, especially this year.
There is no change in CDC’s recommendation on timing of vaccination this flu season. Getting vaccinated in July or August is too early, especially for older people, because of the likelihood of reduced protection against flu infection later in the flu season. September and October are good times to get vaccinated. However, as long as flu viruses are circulating, vaccination should continue, even in January or later.