2016年3月6日 星期日

Why did the flu shot perform so poorly last season?

When a rash of measles outbreaks spawned controversy in America last year, a badly performing flu vaccine also caused concern. The influenza vaccine proved only 23% effective that flu season. In 2014, it was about 60% effective. Why did the flu shot perform so poorly last season? The Economist explains why flu shots are a lottery

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