In remarks reported by Army Radio, Nachman Ash said a single dose appeared "less effective than we had thought", and also lower than Pfizer had suggested.
Comment: It's having an effect, albeit perhaps not the intended effected: HUNDREDS of Israelis get infected with Covid-19 after receiving Pfizer/BioNTech vaccine
By contrast, those who had received their second dose of the Pfizer vaccine had a six- to 12-fold increase in antibodies, according to data released by Sheba Medical Center in Tel Hashomer on Monday.
The issue of some vaccines being less effective after a single dose rather than two is well known, as well as the fact that protection is not immediate. While the first dose can take several weeks to promote an effective antibody response, the second dose can trigger different responses, supercharging the protection. Pfizer itself says a single dose of its vaccine is about 52% effective. Some countries such as the UK have delayed administering their second doses to try to maximise the number of people given a first dose.
Comment: Countries have also delayed the second dose because of severe side effects of the experimental vaccines: Danish govt backs delaying 2nd dose of Covid-19 vaccine like UK, despite safety concerns from Pfizer
Questions over the effectiveness of the vaccine were raised amid reports that thousands of Israelis were still becoming sick after receiving the vaccine, although the public health services head, Sharon Alroy-Preis, said that in most cases this was because the individuals had not built up sufficient antibodies after being inoculated before being exposed to the virus.
The latest figures for Israel, which has implemented one of the fastest national vaccine efforts, underscore the huge challenges still being faced around the globe even in countries with aggressive coronavirus vaccine programmes.
Already more than 2 million Israelis have had their first Pfizer shot, while 400,000 have had a second.
Amid warnings that 30% to 40% of the new infections were being driven by a Covid-19 variant first identified in the UK, the Israeli cabinet was meeting on Tuesday to consider tightening existing restrictions. Some analysts, however, have put the prevalence of the new variant at lower levels.
Comment: There you have it: the vaccine isn't protecting against the current coronavirus, it's unlikely to protect against the 'new strain', the lockdowns are only becoming harsher, and governments aren't even humoring citizens with an end date anymore.
The cabinet had been warned by Ash that the new variant was set to become the main source of infections in Israel within weeks.
The new concern follows the release of data on Monday by Israel's health ministry recording 10,021 infections the previous day, with a positivity rate above the 10% mark for the first time in more than three months, suggesting widespread community transmission.
Comment: Widespread transmission could lead to natural herd immunity, negating any need for a vaccine, although it seems that the hystericized scientific community have conveniently forgotten about that decades old practice.
The rates of infection have undercut the sense of optimism that the Israeli prime minister, Benjamin Netanyahu, has tried to project around Israel's vaccination campaign, for which he has taken credit.
Opening the cabinet meeting on Tuesday, Netanyahu said: "We are in a tight race between the vaccination campaign and the high infection rates in the world due to the mutation." He called for a "last ditch effort" against the virus.
Israel is in the midst of a third lockdown, due to end on Thursday. Other measures under consideration include closing the country's main aviation hub, Ben Gurion international airport, to all except essential flights.
The rise in new cases has provoked a round of finger pointing, not least at lax policing of the ultra-Orthodox community, where some schools have remained open and there have been large gatherings, including a wedding in Bnei Brak on Monday, described as "scandalous", which drew 300 guests before being raided by police.
Describing the impact of the new coronavirus variant, Alroy-Preis told Kan radio that the new variant appeared to be having a significant impact on infections in the ultra-Orthodox community.
"We're seeing very significant and rapid infections and it's really a race between this and the vaccine," said Alroy-Preis, adding that one person who recently returned from the UK had infected 20 to 30 people.