AstraZeneca in the spotlight as booster shot against variants of concern

At a moment in which the world is watching a new peak of COVID-19 cases, preliminary analysis of a study on safetey and immunogenicity indicate that the use of the AstraZeneca vaccine as a booster shot increases the immune response against the variants of concern Beta, Delta, Alpha, and Gamma. An analysis made separately with samples of the research also shows an increased response of antibodies against the Omicron variant, which is behind the new wave of the disease.

Preliminary analysis of a study indicate that the use of the AstraZeneca vaccine as a booster shot increases the immune response against the variants of concern (Image: Peter Ilicciev)

The studies were made on people previously vaccinated with AstraZeneca, manufactured in Brazil by Fiocruz, or mRNA vaccines, and more results should be made public before the first semester of 2022 is over. A separate essay (Phase IV, published as pre-print on The Lancet) also showed that one booster shot of AstraZeneca raised the level of antibodies of subjects who had taken two doses of Coronavac. 

These data come to join evidence that supports the use of AstraZeneca as a booster, regardless of the primary immunization scheme used. AstraZeneca is already submitting this new set of data to health authorities in various countries, at a moment in which some nations, such as the USA, Israel and Brazil itself, are already adopting booster doses.  

“These important studies show that a third dose of Vaxzevria [AstraZeneca] after two initial doses of the first vaccine, or after mRNA or inactivated virus vaccines, strongly increases immunity against COVID-19. The Oxford-AstraZeneca vaccine is a suitable option to increase immunity among the population of countries that take booster programs into account, adding to the protection already shown with the first two doses”, declared Andrew J. Pollard, main researcher and director of the Vaccine Group of the University of Oxford.  

Research lines 

Previous studies already defended the use of a booster dose with AstraZeneca as part of a homologous (all doses of the same vaccine) or heterologous (two doses of one vaccine, booster shot with another) scheme. In a UK study, a booster shot of the AstraZeneca vaccine applied at least six months after the full vaccination scheme significantly increased the level of antibodies and maintained the response of T cells (with immunological functions related to antiviral responses). It also resulted in higher neutralization of the Alpha, Beta and Delta variants when compared with the application of only two doses. Another study, also in the United Kingdom, showed that a third dose of the AstraZeneca vaccine induced a higher immune response in the control against Delta and the original strain after the application of the two doses of AstraZeneca or Pfizer. 

The current study, which showed an increased response against Beta, Delta, Alpha and Gamma, used samples collected 28 days after the administration of the booster shot. The preliminary analysis included individuals who had taken two doses of the AstraZeneca vaccine or of an mRNA vaccine at least three months after the second dose. 

The Phase IV essay evaluated the safety and immunogenicity of one heterologous booster shot by AstraZeneca, one mRNA vaccine (Pfizer/BioNTech), or one vaccine with a recombinant adenovirus vector (Janssen). They were compared to one homologous booster shot using Coronavac in adults in Brazil who had previously received two doses of Coronavac in the six months prior. Between 16 August and 1 September 2021, 1,240 participants were selected to receive the booster shot in the cities of São Paulo and Salvador. 

The first results showed non-inferior levels of anti-spike IgG antibodies 28 days after the booster in the heterologous scheme, when compared with the homologous regime. 

Effect against Omicron 

Another research published in December, carried out independently by researchers of different institutions, including Fiocruz and the University of Oxford, showed that one booster shot with the AstraZeneca vaccine significantly increases the levels of neutralizing antibodies against Omicron. The results were published as pre-print on the bioRxiv platform (Omicron-B.1.1.529 leads to widespread escape from neutralizing antibody responses). Antibodies increased 2.7 times after a third dose with AstraZeneca. 

Data from another laboratory (Broadly neutralizing antibodies overcome Sars-CoV-2 Omicron antigenic shift) neutralizing antibodies overcome Sars-CoV-2 Omicron antigenic shift) reinforce the effect of the AstraZeneca vaccine against Omicron: in this case, individuals vaccinated with the two doses maintained a neutralizing action against the new variant, albeit with some reduction when compared with the original strain. The AstraZeneca/Fiocruz vaccine has proven to be able to induce a diversified and long-lasting response against multiple variants.