CNBC: Pfizer and BioNTech’s Covid-19 vaccine is just 39% effective in Israel where the delta variant is the dominant strain'

However, the two-dose vaccine still works very well in preventing people from getting seriously sick, demonstrating 88% effectiveness against hospitalization and 91% effectiveness against severe illness, according to the Israeli data published Thursday.

Compared to what? I'm assuming tap water is 85% effective against preventing hospitalization.

In a statement to CNBC, Pfizer said it remains confident its two-dose regimen is protective against the coronavirus and its variants.

Still, it said a third dose may be helpful after analysis from its phase three study showed a decline in efficacy against symptomatic infection after four to six months.

Four to six months! That's not very long. That means the world's population needs a booster twice a year.

Pfizer: Initial data of a third dose of the current vaccine demonstrates that a booster dose given at least 6 months after the second dose elicits high neutralization titers against the wild type and the Beta, which are 5 to 10 times higher than after two primary doses.

So two doses is 91% effective supposedly and two doses plus a booster is up to 10 times more effective than that?

Is that even mathematically possible?