Levels and durability of neutralizing antibodies against SARS-CoV-2 Omicron and other variants after ChAdOx-1 or BNT162b2 booster in CoronaVac-primed elderly individuals

Abstract

The outbreak of the SARS-CoV-2 Omicron variant raised the need for vaccine boosting. We evaluated the efficiency of the third booster vaccine, ChAdOx-1 or BNT162b2, in causing a neutralizing antibody (NAb) response and its durability against the Omicron and other variants in elderly individuals previously vaccinated with 2-dose CoronaVac inactivated vaccine. After receiving 2-dose CoronaVac, only 2.2% of subjects had NAbs against the Omicron variant above the cut-off value. Four weeks after boosting, the number of subjects who had NAb levels above the cut-off values in the ChAdOx-1 and BNT162b2 vaccine boosting groups increased to 41.7% and 54.5%, respectively. However, after 12 and 24 weeks of boosting with any vaccines, NAb levels against the Omicron variant dramatically waned. Twenty-four weeks after boosting, only 2% had high levels of NAbs against the Omicron variant. Compared to other variants, the Omicron variant was less responsive to boosting vaccines. The waning rate of NAb levels for the Omicron variant was much faster than that observed in the Alpha, Beta and Delta variants. To combat the Omicron variant, the fourth booster dose is, therefore, recommended for elderly individuals.

Keywords: Booster vaccine; COVID-19; Elderly; Neutralizing antibody; Omicron variant; SARS-CoV-2; Variants of concern.

Fig. 1

Neutralizing antibody response against the Omicron variant. Blood samples were taken after 2-dose CoronaVac (2CoVac) as a baseline before boosting and after boosting with ChAdOx1 (2CoVac + ChAd) or BNT162b2 (2CoVac + BNT) at 4, 12 and 24 weeks. The % inhibition of NAb response against the Omicron and wild type variants are shown. Dot plots represent each individual, and lines connecting the same person for the NAb response against the Omicron (A) and wild type (B) variants are shown. Scatter dots with the median and interquartile range (IQR) of the NAb response against the Omicron variant at the indicated conditions are shown (C). The numbers in parentheses indicate the median value. The Wilcoxon test was used for comparison of the paired samples, *P < 0.05. ***P < 0.001. ****P < 0.0001. ns = not significant. (The results before and 4 weeks after vaccine boosting have been presented in Immun Ageing. 2022; 19 (1):24. https://doi.org/10.1186/s12979-022-00279-8).

Fig. 2

Decrease in neutralizing antibody levels against SARS-CoV-2 variants. The % inhibition (median) of NAb response against the indicated variants at weeks 12 and 24 after ChAdOx1 (A) and BNT162b2 (B) boosting were normalized to the % inhibition (median) of NAb response at week 4 as 100%. The numbers above the bar graph indicate the % of the decrement in NAb levels at the indicated weeks compared to week 4.

Fig. 3

Neutralizing antibody response against the Alpha, Beta and Delta variants. Blood samples were taken after 2-dose CoronaVac (2CoVac) as a baseline before boosting and after boosting with ChAdOx1 (2CoVac + ChAd) or BNT162b2 (2CoVac + BNT) at 4, 12 and 24 weeks. The % inhibition of the NAb response against Alpha (A), Beta (B) and Delta (C) variants is shown. Dot plots represent an individual, and lines connecting the same person are shown. The numbers in parentheses indicate the median value. The Wilcoxon test was used for comparison of the paired samples, **P < 0.01. ***P < 0.001. ****P < 0.0001. The Mann–Whitney U test was used for comparison of the different samples, ^#P < 0.05. ^##P < 0.01. ns = not significant. (The results before and 4 weeks after vaccine boosting have been presented in Immun Ageing. 2022; 19 (1):24. https://doi.org/10.1186/s12979-022-00279-8).