Third Covid Booster Raises Immune Response Against Reinfection: UK Study

A Pfizer COVID-19 vaccine being transferred into a syringe at a mobile vaccination clinic in Worcester, Mass. on Dec. 2, 2021. (Steven Senne/AP)

A U.K. study has found that a third vaccine booster generated a higher level of antibodies to COVID-19 variants 28 days after the third vaccination, compared to individuals who have only completed the Pfizer–BioNTech or the Oxford–AstraZeneca two-shot series (pdf).

“It’s encouraging that a wide range of vaccines, using different technologies, show benefits as a third dose to either AstraZeneca or Pfizer,” stated Saul Faust, NIHR clinical research facility director at University Hospital Southampton NHS Foundation Trust.

“That gives confidence and flexibility in developing booster programmes here in the UK and globally, with other factors like supply chain and logistics also in play,” Faust added.

In the study, 2,878 participants over 30 years of age received a third booster at least 70 days after the primary series.

Seven COVID-19 vaccines, and three with a half dose, were used as a third booster. These vaccines included AstraZeneca, Novavax, Pfizer–BioNTech, France’s Valneva, Janssen’s Johnson & Johnson, Moderna, and Germany’s Curevac.

Among those who were primed with two shots of AstraZeneca, a third booster with Moderna generated the highest level of antibodies to the Delta variant, at a level 27-fold stronger than that of the control group.

Even Valneva, which generated the lowest level of antibodies among the vaccines, gave rise to nearly two times the level of antibodies compared to the control.

Similar results were found in individuals primed with the Pfizer–BioNTech series, with Moderna generating a 12-fold increase in antibody levels to the Delta variant; while no significant differences were found between Valneva and the control group.

Among all mRNA vaccines, Moderna was also noted to be “most reactogenic,” that is, most likely to cause a common adverse reaction.

While the “importance of antibody-mediated immunity in protection against SARS-COV-2 infection has been demonstrated” in primates and humans, researchers said that it remains unclear whether antibodies protect one from an asymptomatic infection.

Except for AstraZeneca and Valneva, all other vaccines induced a strong immune T-cell response when given as a third dose in individuals who have completed a two-shot AstraZeneca series.

Those who have received two doses of the Pfizer–BioNTech developed a strong T-cell response to all vaccines apart from Valneva.

While the study describes T-cell responses to be “important in controlling disease severity,” a link between symptomatic disease and the level of T-cell response has “yet been demonstrated.”

“T-cell activity appears minimally affected by spike antigen mutations and responses remain against variants of concern, even though neutralizing antibody levels are reduced,” the study stated.

While experts have voiced concerns over antibodies not being able to bind and neutralize mutated viruses of new variants with a mutated spike protein, BioNTech CEO and co-founder Dr. Ugur Sahin told the Wall Street Journal last month that it will be difficult for Omicron to escape the “second level of immune response” conferred from T cells.

The Lancet study recorded 1,306 adverse events from 912 participants. Severe reactions were reported in less than 5 percent of participants across all vaccine groups.