Async method call on ComboBox selection with MVVM

I'm facing a problem with displaying graphs filtered by ComboBox selection without having the UI lock up. The statistic filtering is quite heavy and needs to run async. This works fine all up until I try to call FilterStatisticsAsync and MonthSelectionChanged from the Property setter. Does anyone have a good tip on how to solve or work around this?

The XAML looks like this:

        <ComboBox x:Name="cmbMonth"
                  ItemsSource="{Binding Months}" 
                  SelectedItem="{Binding SelectedMonth }"
                  IsEditable="True"
                  IsReadOnly="True"

And the ViewModel property setter like this:

    public string SelectedMonth
    {
        get { return _selectedMonth; }
        set { SetProperty(ref _selectedMonth, value); LoadStatisticsAsync(); MonthSelectionChanged(); }
    }

SetProperty derives from a base class which encapsulates INPC like this:

        public event PropertyChangedEventHandler PropertyChanged = delegate { };

        protected virtual void SetProperty<T>(ref T member, T value, [CallerMemberName] string propertyName = null)
        {
            if (Equals(member, value))
                return;

            member = value;
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }