The immune response elicited by an inactivated SAR-CoV-2 vaccine

By Colin Lightfoot, M.Sc. Infection and ImmunityReviewed by Benedette Cuffari, M.Sc.Nov 10 2021

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative virus responsible for the coronavirus 2019 (COVID-19). As of November 10, 2021, there have been over 250 million confirmed cases of COVID-19 and over 5 million deaths. In addition to those directly affected by COVID-19, the current pandemic has also caused significant disruption to global health services and the global economy.

Due to SARS-CoV-2 being so highly communicable and the severe outcomes associated with the disease, the primary strategy that can help control the pandemic is the development of effective vaccines. To date, 184 and 112 COVID-19 vaccine candidates are in pre-clinical and clinical development phases. In several countries around the world, emergency authorization has been granted to at least seventeen different COVID-19 vaccines.

Study: Human IgM and IgG Responses to an Inactivated SARS-CoV-2 Vaccine. Image Credit: Lightspring / Shutterstock.com

It has been suggested that mixing different types of COVID-19 vaccines may elicit a more robust immune response as compared to when a single type of vaccine is used alone. However, the influencing factors on the immunogenicity induced by available vaccines have not yet been fully explored. In a recent Current Medical Science study, a team of researchers from a variety of Chinese institutions assessed antibody responses to the inactivated SARS-CoV-2 vaccine among vaccine recipients in Shenzhen, China.

About the study

The current study was a retrospective analysis that involved patients between the ages of 18-60 who were not infected with SARS-CoV-2 at the time of the study. All the participants were administered the recommended two doses of the SARS-CoV-2 inactivated Sinovac vaccine.

Participants were excluded from this study if they had recently traveled outside of China or to regions with a high prevalence of COVID-19, had confirmed contact with an infected individual, and/or exhibited symptoms such as fever, cough, and sore throat, and rheumatic immune conditions.

A total of 97 participants were recruited and vaccinated with an inactivated SARS-CoV-2 vaccine for the current study between June 19, 2021 and July 2, 2021. The mean age within the cohort was 35.6 years, with 37 participants aged between the age of 20-30 (38.2%), 34 participants aged between 31-41 (35.0%), 15 participants aged between 42-52 (15.5%), and 10 participants older than 53. The cohort was comprised of a slightly higher number of female participants, with 62.9% female and 37.1% male.

The immunoglobulin G (IgG) antibody level response post-vaccination with the second dose was 74.2%. However, only 3.1% of the participants were observed to elicit an IgM antibody response following the second dose of vaccine. After the second dose of the vaccine, the results showed that the IgG antibody level was significantly higher than the IgM antibody level.

IgM and IgG antibody levels following the second vaccine were compared in recipients with respect to age and sex to examine the influencing factors on the vaccine-induced immunogenicity. The results showed that sex was not related to anti-IgM and anti-IgG levels in all participants following the second dose of the inactivated SARS-CoV-2 vaccine.

Although there were no statistically significant variations observed in IgM and IgG antibody levels within the different age groups, mean anti-IgG levels in the two older groups were significantly lower when compared to the groups containing younger participants. There was a significantly lower level of antibodies observed at over 42 days when compared to 0-20 days and 21-31 days following the second dose of vaccine.

Implications

The rapid development of SARS-CoV-2 vaccines should be addressed with some important questions. A large concern is the durability of the vaccine-elicited immune protection over extended periods of time post-vaccination. Another concern is how effective a booster dose will be in prolonging the duration of immunity against SARS-CoV-2.

The inactivated SARS-CoV-2 vaccine utilized in this study successfully induced an anti-SARS-CoV-2 IgG antibody response in healthy individuals who were above the age of eighteen. This response elicited may be influenced by age and detection time following vaccination.