Effect of homologous or heterologous vaccine booster over two initial doses of inactivated COVID-19 vaccine

ABSTRACT

Introduction

Inactivated vaccines were delivered to low- and middle-income countries during the early pandemics of COVID-19. Currently, more than 10 inactivated COVID-19 vaccines have been developed. Most inactivated vaccines contain an inactivated whole-cell index SARS-CoV-2 strain that is adjuvant. Whole virions inactivated with aluminum hydroxide vaccines were among the most commonly used. However, with the emerging of COVID-19 variants and waning of the immunity of two doses of after 3 months, WHO and many local governments have recommended the booster-dose program especially with heterologous platform vaccine.

Area Covered

This review was conducted through a literature search of the MEDLINE database to identify articles published from 2020 to 2023 covered the inactivated COVID-19 vaccines primary series with homologous and heterologous booster focusing on safety, immunogenicity, efficacy, and effectiveness.

Expert opinion

The inactivated vaccines, especially whole virion inactivated in aluminum hydroxide appeared to be safe and had good priming effects. Immune responses generated after one dose of heterologous boost were high and able to preventing severity of disease and symptomatic infection. A new approach to inactivated vaccine has been developed using inactivating recombinant vector virus-NDV-HXP-S vaccine.

KEYWORDS:

• Primary series
• inactivated COVID-19 vaccine
• heterologous boost
• variant of concerns
• new generation inactivated vaccine

Article highlights

• Inactivated vaccines - an aluminum-hydroxide-adjuvanted, inactivated whole virus vaccine(Coronavac/Sinovac) and BBIBP-CorV/Sinopharm were delivered to low- and middle-income countries during the early pandemics of COVID-19 in 2021.

• Two doses of immunity were waning after 3 months.

• The heterologous regimens include boosting with vector-based (Ad26.COV2-S, ChAdOx1 nCoV-19), mRNA-based (BNT162b2, mRNA-1273), and subunit and recombinant protein COVID-19 vaccines.

• The inactivated vaccine appeared to have good priming effects which were able to raised the immune responses up after one dose of heterologous boost especially in preventing severity of disease against both Delta and Omicron (BA.1) variants.

• New concept of inactivated vaccine by inactivating recombinant vector virus using a recombinant vector inactivated platform, the NDV-HXP-S COVID-19 (Wuhan-Hu-1 strain) vaccine has no safety concerns and able boost the immune response similar to the vector- based platform.

Declaration of interest

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

Reviewer disclosures

Peer reviewers on this manuscript received honoraria for their review work. Peer reviewers on this manuscript have no other relevant financial or other relationships to disclose.

Author contribution statement

I confirm all authors should have (1) substantially contributed to the conception and design of the review article and interpreting the relevant literature, and (2) been involved in writing the review article or revised it for intellectual content.

Additional information

Funding

The project is funded by the National Research Council Thailand (NRCT) and Mahidol University [Fund No. N42A660809].