Vodafone said it remained committed to floating the Australian operation and would "continue to monitor market conditions in order to assess the optimal timing for the transaction".

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"It's going to be a few years until we really know whether or not people need another booster dose, and what is the optimal timing for that booster dose" for Tdap, because it is so new, Martin said.

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There is little rigorous research on the optimal generation and coordination of customer leads and timing of subsequent calls, it said.

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For timing, PostRocket analyzes pages with similar characteristics, including demographics, to provide recommendations of optimal times to post.

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