Despite the difficulties, researchers continue to investigate several approaches in the quest for a successful vaccine. At present, however, it seems unlikely that a vaccine will be produced soon.
और अगर ऐसी असरदार वैक्सीन बन भी जाए, तब शुरू होगा एक और भी मुश्‍किल, खर्चीला और काफी खतरनाक दौर ।