Question: when was the chickenpox vaccine introduced in the united states
[{'answer': '1984', 'provenance': [{'wikipedia_id': '8649736', 'title': 'Varicella vaccine', 'start_paragraph_id': 4, 'start_character': 62, 'end_paragraph_id': 4, 'end_character': 66, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '8649736', 'title': 'Varicella vaccine', 'start_paragraph_id': 4, 'start_character': 0, 'end_paragraph_id': 4, 'end_character': 256, 'bleu_score': 0.953991849837532, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 16583375728640765258}, 'section': 'Section::::Abstract.'}]}]