Additional COVID-19 Booster Dose Strengthens Waning Immunity Against Omicron Subvariants

Although the protective immunity generated by the primary COVID-19 vaccine series or prior infection has been reduced by Omicron subvariants, a booster dose, regardless of the type of vaccine, elicited neutralizing antibodies against all the Omicron subvariants, according to a new study published in Science.

Investigators assessed a comprehensive panel of vaccines available in the United States and worldwide, as well as immunity acquired through previous infection.

"The development of lifesaving vaccines is regarded as one of humanity's greatest medical and scientific achievements, which is exemplified by COVID-19 vaccines," the investigators said in a statement.

The study’s findings coincide with the US government considering recommendations of a second booster dose for adults under 50 years of age due to rising infection rates and the enhanced transmissibility of Omicron BA.5. The findings are also consistent with other research that found a third vaccine dose expands existing memory B cells that are specific for the spike protein of the SARS-CoV-2 virus and induces new memory B cells.

Additionally, it leads to the production of antibodies with enhanced potency against Omicron subvariants. Investigators first examined the functional impact of the mutation in the Omicron subvariant spike proteins and found that the ability of the Omicron BA.5 spike to bind with its host receptor was more than 6 times stronger than the ancestorial strain.

However, they found that all subvariants were slower at the next major step after binding with the receptor, which is fusing with the membrane on the host cell. The stronger binding could help the subvariants compensate for the capacity to fuse with the host cells, according to the investigators.

They also evaluated the neutralizing activity elicited by the vaccines or by prior infection in human plasma samples against various Omicron subvariants. Some samples came from individuals who had a COVID-19 infection early in the pandemic before vaccines were available. Out of 24 early pandemic infections, 5 individuals had detectable neutralizing activity in their plasma against any of the 4 Omicron sub-lineages that were tested, and investigators reported that their response was very weak.

To evaluate the subvariant neutralizing antibodies, investigators used the Moderna, Pfizer, Novavax, Janssen, AstraZeneca, Sinopharm, and Sputnik V vaccines, with all but the Janssen vaccine consisting of a primary series of 2 doses.

Investigators said that there was a consistent but subtle effect for BA.1 compared to BA.2 and BA.2.12.1. They also said that there was even more of an effect for BA.4/5.

The findings confirmed that the BA.5 subvariant will be most immune to vaccines to date.

"The marked improvement in plasma neutralizing activity for subjects that received a booster dose over those that did not highlights the importance of vaccine boosters for eliciting potent neutralizing antibody responses against Omicron sub-lineages," the investigators said in the statement.

They added that they believe the availability of several different vaccines could help to create a more robust cross-reactive cellular immunity against subvariants.

Reference

Booster shots offset some of Omicron immune evasion tactics. News release. Science Daily. July 19, 2022. Accessed July 25, 2022. https://www.sciencedaily.com/releases/2022/07/220719102321.htm