When the US government began shipping Covid-19 vaccines in December, state health providers could not administer shots fast enough to keep pace with deliveries and millions of doses sat waiting for arms.

Two months later, the situation has reversed. Supply constraints are slowing ambitious vaccination programmes, as massive sites capable of putting shots into thousands of arms daily in states including New York, California, Florida and Texas, as well as hospitals and pharmacies, beg for more doses.

Nearly a dozen state and local officials told Reuters they could vaccinate up to four times more people, but federal vaccine shipments remain frustratingly small.

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