"A huge drop": 40-fold decline in neutralization by Pfizer vaccine against Omicron in first study

"A huge drop": 40-fold decline in neutralization by Pfizer vaccine against Omicron in first study
AP Photo/Ted S. Warren

Virologists and other infectious disease experts are trying to put their most positive spin on these new results but one, Florian Krammer, couldn’t muster the energy. “That is a huge drop,” he said of the numbers showing Pfizer’s vaccine much weaker against the new South African Omicron than everyone hoped. “Omicron sucks. I don’t like it,” he added.

Many things can be said about the data but no one can say it was a surprise. The reason there was such a fuss among experts on Thanksgiving Day about the variant is that its spike protein had a mind-boggling array of mutations on it, many more than virologists would have expected from a variant at this stage of the pandemic. The vaccines train the immune system to produce antibodies targeted at the spike protein of the original Wuhan virus. The more different a variant’s spike is, the more trouble those antibodies will have identifying it. Omicron is very, very different.

Scientists in South Africa took plasma from a small number of people, some of whom have received Pfizer’s vaccine and some of whom had COVID awhile ago and were then vaccinated with Pfizer. Result: The plasma from the latter group with “hybrid immunity” did well against Omicron. The plasma from the first group had more trouble. Note the graph at the bottom here:

Both groups took a hit but the group with hybrid immunity started from a much higher baseline of protection. Scientists have known for months that hybrid immunity is the gold standard, conferring superhuman protection even against variants (like Omicron until a month ago) that haven’t evolved yet. That’s borne out in these results.

As for the gigantic share of the population that’s had two shots but hasn’t been infected with COVID: Welp.

Reactions among experts besides Krammer have taken three forms. The first acknowledges that a 40-fold drop in neutralization isn’t great while adding that it could be worse. The second reminds everyone, importantly, that there’s more to immunity than antibody neutralization. The memory B cells generated by the vaccines should help limit severe disease in the vaccinated even if there are lots more breakthrough infections. The third emphasizes that the tests in the new study were performed on people who’d received only *two* doses of Pfizer, not three. It must be the case that people who’ve been boosted are better protected against the variant. Conceivably they might be as well protected as those with hybrid immunity are…

…but how long will the immunity conferred by a booster last? What if it isn’t as robust against Omicron as hybrid immunity is? And what do we do about the fact that less than a quarter of fully vaccinated Americans and less than half of fully vaccinated senior citizens have received boosters so far?

Suddenly a lot is riding on the early assessments that Omicron is much less severe than previous variants like Delta. If it spreads as quickly as it appears to and it punches through immunity to the degree the new study suggests, you can see why some experts not normally given to panic are “seriously worried” about it.

Again, though, no one can call this a surprise. The day after Thanksgiving, a virologist noted that her team had recently designed a mutant spike protein and tested it against plasma from people with various forms of immunity. As chance would have it, that lab-created spike had many of the same mutations that Omicron’s spike does. Results: Bad.

One research laboratory confirmed that assessment, finding that antibodies had almost as much trouble binding to Omicron’s spike as they did binding to the lab-created mutant:

The feds are destined to react to today’s study by urgently encouraging all Americans to get boosted as quickly as possible, maybe even trying to fold boosters into the current vaccine mandates to encourage compliance. We might still be bailed out by Omicron proving to be far less virulent than Delta is. But we might not.

Read this thread from a rare expert who’s been optimistic about Omicron from the start. He’s hopeful that boosters will provide meaningful protection. And note that BioNTech, which developed Pfizer’s vaccine, is coming with data of its own tomorrow about the vaccine’s efficacy. “I would be more optimistic,” said the head of the company about what he expects the results to be.

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Jazz Shaw 1:01 PM on April 01, 2023