Jerusalem, Jul 25 (IANS): New data from Israel and the UK is showing a contradictory picture on the effectiveness of Pfizer-BioNTech's Covid-19 vaccine in fighting off the Delta variant, the media reported.

A new Health Ministry statistics from Israel indicated that, on average, the Pfizer-BioNTech shot is now just 39 per cent effective against infection, while being only 41 per cent effective in preventing symptomatic Covid-19.

Previously, the Pfizer-BioNTech vaccine was well over 90 per cent effective against infection, reports The Times of Israel.

Meanwhile, a new UK study published this week in The New England Journal of Medicine found the same vaccine to be 88 per cent effective in preventing symptomatic Covid-19 -- more than twice the rate found in the Israeli data.

Israel's research agreed, at least, that the shot was highly effective in avoiding serious illness, at 91.4 per cent effectiveness, the report said.

Some analysts have warned that the figures on vaccine effectiveness are prone to major inaccuracies because of a range of factors, including questions over whether there is accurate data on infection levels among the non-vaccinated, which is vital for such stats.

The Israeli statistics also appeared to paint a picture of protection that gets weaker as months pass after vaccination, due to fading immunity.

People vaccinated in January were said to have just 16 per cent protection against infection now, while in those vaccinated in April, effectiveness was at 75 per cent.