【《We Chinese in America》Media Editor Tang Zhao, September 17, 2022】The updated boosters target the newer, widely spread Omicron subvariants of the COVID-causing virus, BA.4 and BA.5, as well as the early 2020 form of the microbe, known as the ancestral strain. This is the first change for the Pfizer and Moderna shots since they were introduced two years ago, when they contained only genetic material from the ancestral form of the virus. (Image from Getty Images)

The new booster shots are expected to trigger a better immune response against the new subvariants.  As people congregate closer together in winter months, they’re more likely to spread microbes between them.

The new vaccine formulations, which are known as bivalent shots because they contain components of two versions of the virus. The Pfizer-BioNTech and Moderna COVID vaccines contain snippets of viral genetic material called mRNA. Once injected, it can’t create a whole virus, but it does tell cells to build one isolated piece, the infamous spike protein found on the surface of SARS-CoV-2. When the human immune system detects that protein, it starts to produce antibodies and activate other immune cells that can fight the actual virus.

The updated boosters contain mRNA instructions for both the ancestral spike protein and the one on Omicron BA.4 and BA.5. (The protein from those two subvariants is extremely similar.) This is why the new shots induce a broader immune response. All of the other ingredients—such as lipids, salts and acids, which help protect the mRNA and deliver it to our cells, balance acidity and maintain the stability of the vaccine—haven’t changed from the original formulation. The overall dose of each updated booster is also the same as the original boosters.

In a clinical preprint study evaluating one of Moderna’s earlier bivalent booster versions—which was made with the ancestral form and the original Omicron variant, called BA.1—participants who received the booster had a 7.1-fold rise in neutralizing antibody levels against Omicron. The ones who received the ancestral-only booster had a smaller, 3.8-fold rise in neutralizing antibody levels. An advantage was also seen in neutralizing antibody levels against Omicron BA.4 and BA.5.

A similar result was achieved by an earlier bivalent booster developed by Pfizer and BioNTech. It led to a 9.1-fold rise in neutralizing antibody levels against the original form of Omicron, compared with a 5.8-fold rise obtained by the ancestral-only booster. A smaller advantage was seen in neutralizing antibody levels against BA.4 and BA.5.

Clinical trials of the earlier bivalent booster versions show that they have a risk profile very much like the original vaccines and boosters. The clinical study that evaluated the earlier version of Moderna’s bivalent booster showed that the most commonly reported side effects were typical, including pain, redness and swelling at the injection site, fatigue, and some nausea and fever. An early version of a bivalent shot from Pfizer and BioNTech had a similar profile.

(Source: Scientific American)

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