erro para grafico confirmed_by_country[last_date].plot()

Olá, Não estou conseguindo gerar o gráfico

confirmed_by_country[last_date].plot()

Aqui está o código que usei para gerar

last_date = confirmed_by_country.iloc[:,-1] 

e

confirmed_by_country = confirmed.groupby('Country/Region').sum()

E abaixo é o erro que aparece

---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
<ipython-input-41-79adff188095> in <module>
      1 plt.figure(figsize=(20,5))
----> 2 confirmed_by_country[last_date].plot()
      3 plt.title('Confirmados por país')

C:\ProgramData\Anaconda3\lib\site-packages\pandas\core\frame.py in __getitem__(self, key)
   2804             if is_iterator(key):
   2805                 key = list(key)
-> 2806             indexer = self.loc._get_listlike_indexer(key, axis=1, raise_missing=True)[1]
   2807 
   2808         # take() does not accept boolean indexers

C:\ProgramData\Anaconda3\lib\site-packages\pandas\core\indexing.py in _get_listlike_indexer(self, key, axis, raise_missing)
   1550 
   1551         self._validate_read_indexer(
-> 1552             keyarr, indexer, o._get_axis_number(axis), raise_missing=raise_missing
   1553         )
   1554         return keyarr, indexer

C:\ProgramData\Anaconda3\lib\site-packages\pandas\core\indexing.py in _validate_read_indexer(self, key, indexer, axis, raise_missing)
   1637             if missing == len(indexer):
   1638                 axis_name = self.obj._get_axis_name(axis)
-> 1639                 raise KeyError(f"None of [{key}] are in the [{axis_name}]")
   1640 
   1641             # We (temporarily) allow for some missing keys with .loc, except in

KeyError: "None of [Int64Index([ 37596,   7380,  38583,    989,   1906,     93, 294569,  41663,\n             23558,  23370,\n            ...\n            320343,   1440,  35329,  33755,    964,  16534,     10,   1869,\n              9343,   5261],\n           dtype='int64', length=188)] are in the [columns]"

<Figure size 1440x360 with 0 Axes>