Israeli data: A fourth vaccine dose doesn't stop infection by Omicron

AP Photo/Matt Rourke

It’s almost a relief to read this. Obviously it would be better if the fourth dose successfully shut down the new variant.

But it’s nice to finally be able to get off the vaccine treadmill. For a little while.

We already know from Israel’s ongoing trial that a fourth dose does boost antibodies — fivefold, to be exact. For that reason, the researchers in charge continue to recommend the second booster for at-risk populations like senior citizens and the immunocompromised. The more antibodies you have, the better your chance of fighting off an infection before it gets rolling.

But it turns out your chances aren’t much better after the fourth dose. And since antibodies begin to wane before long (a few months, maybe?), the mild benefit from each successive dose would necessarily be temporary. Which leaves the case for a second booster thin.

“The vaccine, which was very effective against the previous strains, is less effective against the Omicron strain,” Prof. Gili Regev-Yochay, a lead researcher in the experiment said.

“We see an increase in antibodies, higher than after the third dose,” Regev-Yochay said. “However, we see many infected with Omicron who received the fourth dose. Granted, a bit less than in the control group, but still a lot of infections,” she added…

Regev-Yochay added that it is still probably a good idea to give a fourth shot to those at higher risk, but intimated that perhaps the current campaign, which also offers the jab to the over-60s, should be amended to only include even older groups. She did not elaborate.

As it turns out, we do have an over-60 cohort here in the U.S. that’s in urgent need of extra help fighting off Omicron. Even a mild and temporary boost in protection for nursing-home residents might save lives:

Nursing homes reported a near-record of about 32,000 COVID-19 cases among residents in the week ending Jan. 9, an almost sevenfold increase from a month earlier, according to the Centers for Disease Control and Prevention.

A total of 645 COVID-19-related deaths among residents were recorded during the same week, a 47% increase from the earlier period. And there are fears that deaths could go much higher before omicron is through

Nursing homes are also working to drive up vaccination numbers, especially for boosters. Sixty-three percent of nursing home residents nationally have received an extra dose.

A 63 percent booster rate for the most vulnerable segment in society is piss-poor, made worse by the fact that just 29 percent of nursing-home staff are boosted. How will we get residents a fourth dose when more than a third are still lacking their third?

The Israeli booster data raises two questions. First, if a fourth dose of a vaccine based on the ancestral Wuhan strain is no longer adding much in terms of protection, is it time for Pfizer and Moderna to go all-in on an Omicron-specific booster? To do that, they’d need to switch over their manufacturing capacity from producing the current vaccine to the new vaccine, which would leave them exposed if Delta or some new variant that’s closer genetically to the original virus comes roaring back and supplants Omicron. If you think of SARS-CoV-2 as a tree trunk and its variants as branches, the vaccine manufacturers would essentially be deciding to focus on a single branch instead of continuing to target the tree at its trunk.

On the other hand, what if that single branch is the only part of the tree that’s still alive?

Omicron is now responsible for more than 99 percent of cases in the U.S. But is that because the number of Delta cases has fallen, with that variant driven to near-extinction by the natural immunity generated by Omicron infections? Or is Delta still circulating abundantly and there are simply 99 times as many cases caused by the new, hyper-infectious variant? Much depends on the answer in deciding whether to shift to an Omicron-specific booster.

Relatedly, a new study done in mice suggests that being infected by Omicron does protect you against other variants like Delta — but only if you’ve been vaccinated. If Omicron is your first exposure to the virus, Delta remains a threat:

That makes sense intuitively. If you’ve had your shots, your immune system has already gained considerable knowledge about the spike protein on Wuhan-style strains of the virus, like Delta. Getting infected by Omicron gives it more information about the entire virus, which should mean you’ll produce more sophisticated antibodies to neutralize the virus going forward. Whereas if an Omicron infection is your first exposure to the virus, you may not have “learned” enough about it yet to fight off a Delta infection efficiently.

The other key question in light of the new Israeli data is whether a fourth dose might meaningfully improve the protection you get from severe disease even if it doesn’t do much to protect you from infection. Conceivably a fourth exposure to the spike protein via vaccination would further educate your immune system about the coronavirus and how to beat it back quickly, before it causes an illness bad enough to send you to the hospital. But that raises a secondary question: How much better protected could someone who’s had three doses realistically be? Just look at this data.

In Switzerland, only one in 400,000 boosted people are dying. If a fourth dose improved those numbers to one in 500,000, say, would it be worth it? I’m guessing most Americans will say no.