It seems like it was just a week ago we were hearing that boosters might not be needed because Pfizer provides durable protection against the virus.

Come to think of it, it was a week ago. (Well, nine days.)

This new study will get the booster chatter going again. It also explains why Anthony Fauci and Rochelle Walensky have begun nudging even vaccinated people to mask up in communities where the vaccination rate is low. Pfizer’s amazing vaccine turns out to be notably less effective at preventing infection by the hyper-contagious B.1.617 “Delta” variant than it was against standard SARS-CoV-2. Importantly, though, it’s not notably less effective at preventing serious illness caused by Delta. It should keep you out of the hospital if you’re unlucky enough to contract that variant.

But Fauci and Walensky realize now that, to avoid infection in the first place, vaccinated people may need to do a little more than just get their shots.

The vaccine protected 64% of inoculated people from infection during an outbreak of the Delta variant, down from 94% before, according to Israel’s Health Ministry. It was 94% effective at preventing severe illness in the same period, compared with 97% before, the ministry said…

With more than 80% of Israeli adults fully vaccinated with two doses of the Pfizer vaccine, Israeli health officials are paying greater attention to how many develop serious illness. That number currently stands at 33, with the majority coming from the elderly immunocompromised population, according to health officials…

Israel may have specific population characteristics that could influence the survey’s results. Those would include having the youngest population of any country in the Organization for Economic Cooperation and Development, with the youth on average less inoculated and gathering in schools, the possibility of waning immunity since many Israelis have been vaccinated for nearly six months, and the fact that Israel removed nearly all public-health restrictions before the recent outbreak.

A big decline in the vaccine’s ability to prevent infections coupled with basically no decline in its ability to prevent serious illness helps explain the data we’re seeing in Israel and the UK, where Delta is also rampant. In Israel cases are at their highest point in three months, rising from practically nothing in May to several hundred daily…

…and yet deaths are cruising along at zero:

One recent Israeli analysis found that in previous waves some 2.5 percent of people infected became seriously ill. In the current gathering wave, despite Delta’s fearsome attributes, just 0.5 percent are. The vaccines are working in the most critical metric.

The UK numbers are more dramatic. Cases are up, up, and away, reaching their highest level since the brutal winter wave of late January…

…but deaths have barely budged from where they’ve been since mid-April:

Britain’s health secretary projected today that cases could double in the next two weeks and eventually reach 100,000 daily, a number the country has never approached and which would translate into 500,000 daily cases per capita in the U.S. But they’re willing to tolerate a “casedemic” in the name of reopening so long as their hospital system isn’t under pressure. One top UK epidemiologist calculated that 50,000 daily cases in previous waves typically meant 500 deaths per day but in the post-vaccine era it should mean only 50 per day — even with Delta responsible for nearly all infections.

There’s no mystery as to why cases and deaths no longer track. Older people in Israel and the UK are nearly all vaccinated and the vaccines are keeping them out of the hospital, even when Delta manages to break through their immunity and infect them. Meanwhile, younger people are less vaccinated and are being infected more frequently but their immune systems are naturally strong enough due to age to fight off the virus. Result: Few hospitalizations and deaths in either group. Essentially, the vaccines have turned vaccinated older adults into the immune equivalent of younger unvaccinated ones.

Although I reserve the right to revisit that analysis in a few weeks, if it turns out that the low daily death numbers in both countries are due merely to deaths being a lagging indicator after a new wave of cases develops.

If you want an ominous spin on what the new Israeli data *might* mean, here’s former Biden COVID czar Andy Slavitt weighing in. What if the surge of cases in Israel isn’t due solely to Delta being more contagious? What if it’s due to Israelis losing their immunity?

Instead it’s possible that this is a signal that immunity could simply be waning in certain populations. Recall that Israelis vaccinated before the US. So our first sign of a vaccine waning will likely be seen in Israel.

Could this be an early sign of waning immunity? 4/

— Andy Slavitt 🇺🇸💉 (@ASlavitt) July 6, 2021

Whether 65 and above or 50 and above, the first recommendation about boosts is likely to be for “older” people.

(At 54 I take some issue with the characterization of either of these groups as “older.” I am going with “more seasoned” or simply “wiser.”) 🙂 6/

— Andy Slavitt 🇺🇸💉 (@ASlavitt) July 6, 2021

Uh, well, yes, it’s wonderful that we’re able to boost waning immunity with nothing more than a shot of the vaccines we already have on hand. But no one wants to have to get a shot every six months, especially when the side effects appear to become more severe with each additional dose. And again: Just nine days ago we were rejoicing over a study pointing to long-lasting immunity from the mRNA vaccines. If that study is accurate, why would Israelis’ immunity be in decline after six months? And how can their immunity be waning if hospitalizations and deaths are still near zero? Does Slavitt mean to suggest that that could change soon, and rapidly, without a booster?