Doesn’t seem to be associated with severity of initial illness.

Long COVID is less common if you are vaccinated already. In a community based study of adults aged 18 to 69 years infected with SARS-CoV-2 before vaccination against covid-19, the odds of experiencing long covid symptoms decreased by an average of 13% after a first covid-19 vaccine dose, with a further 9% decrease in the odds of long covid after a second dose. [https://doi.org/10.1136/bmj-2021-069676] 

If you already have long COVID, further COVID immunisations seem to be beneficial, rather than harmful:

• In a non-controlled study of 900 social media users with long COVID, more than half experienced an improvement in symptoms after vaccination compared with 7% who reported a deterioration.19
• A study of 44 vaccinated patients and 22 unvaccinated controls previously admitted to hospital with covid-19 in the UK, which inevitably had limited power to detect clinically relevant effects, found no evidence for vaccination being associated with worsening of long covid symptoms or quality of life.20
• A French study of 455 self-selected participants found reduced long COVID symptom burden and double the rate of remission at 120 days in vaccinated participants compared with unvaccinated controls.

All about symptoms, excluding treatable conditions, then self management. For adults: