Celery - Cannot fetch task results

I'm using the Django ORM/Cache as the result backend for celery. I can see that django_celery_results_taskresult table is created in the database. After the tasks are finished the results are also inserted in the database which can be viewed from MySQL. But when I try to access the results using AsyncResult and task ID from django manage.py shell I get the following error.

>>> AsyncResult.get('88e4d870-1a2b-4675-8f7c-1eacb7199bda')
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/root/vms/lib/python3.6/site-packages/celery/result.py", line 199, in get
    if self.ignored:
AttributeError: 'str' object has no attribute 'ignored'
>>> AsyncResult('88e4d870-1a2b-4675-8f7c-1eacb7199bda').get()
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/root/vms/lib/python3.6/site-packages/celery/result.py", line 224, in get
    on_message=on_message,
  File "/root/vms/lib/python3.6/site-packages/celery/backends/base.py", line 470, in wait_for_pending
    no_ack=no_ack,
  File "/root/vms/lib/python3.6/site-packages/celery/backends/base.py", line 773, in _is_disabled
    raise NotImplementedError(E_NO_BACKEND.strip())
NotImplementedError: No result backend is configured.
Please see the documentation for more information.

My celery.py file is:

from __future__ import absolute_import, unicode_literals
from celery import Celery
import os

os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'vms.settings')

app = Celery('vms', broker='redis://localhost', include=['cve.tasks','cpe.tasks'])

app.conf.update(
    result_backend='django-db',
    timezone = 'Asia/Kolkata'
)

if __name__ == '__main__':
    app.start()

I've included django_celery_results in settings.py INSTALLED_APPLICATIONS.

I find it weird that the results get inserted into the database but cannot be retrieved.