Last week, a tweet from Israel’s Ministry of Health sent the world into a tizzy. It said that in Israel, the Pfizer vaccine was only 64% percent effective against symptomatic COVID-19 infection, down from 97% in May. Now, Pfizer is suggesting that a third shot—a booster—is needed, though experts disagree.
The confusion stems from conflicting data on exactly how effective COVID-19 vaccines are against the latest and most troublesome SARS-CoV-2 variant, Delta (B.1.617.2). The effectiveness rate is derived by analyzing the total number of breakthrough infections, or the number of people who are vaccinated but contract COVID-19 anyway. The reason for the diverging figures may be that it’s difficult to calculate vaccine effectiveness in an ever-changing environment, where a new variant is spreading while vaccination rates slowly tick upward. The other reason may be that not all the data is in yet.
The Delta variant is extremely transmissible, 60% more than the original COVID-19…
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Source : fastcompany.com
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