What IS behind Britain's Covid vaccine slowdown?

A vaccine dose delivery schedule published by the Scottish Government in January suggests that officials knew there would be a dip in vaccine supply in February before a spike in availability in March. https://www.dailymail.co.uk/news/article-9294749/What-Britains-Covid-vaccine-slowdown.html?ns_mchannel=rss&ns_campaign=1490&ito=1490