Europe had “lacked ambition” in its vaccine efforts from the outset, no less a source than Mr Macron told a Greek television programme on March 24th.

由于no less a source 这个词组含有比较级 less，应把整个比较结构包含在内。

本句 no less a source than Mr Macron told a Greek television programme on March 24th ，是前句的描写性非限制性定语。可以扩展为定语从句：

Europe had “lacked ambition” in its vaccine efforts from the outset, which was no less a source than Mr Macron told a Greek television programme on March 24th. （which 指代前面句子的内容）

分析一下no less a source 的含义。a source 指“来源；源头”，no less a source 意思是“差不多一个来源”，引申为“同出一辙”。

【翻译】欧洲从一开始就在疫苗方面 “缺乏雄心壮志”，正如马克龙3月24日在希腊一档电视节目中所说的那样。（与马克龙3月24日在希腊一档电视节目中所说的同出一辙）