Immunogenicity of BNT162b2 COVID-19 vaccine in New Zealand adults

Abstract

Background: There is very little known about SARS-CoV-2 vaccine immune responses in New Zealand populations at greatest risk for serious COVID-19 disease.

Methods: This prospective cohort study assessed immunogenicity in BNT162b2 mRNA vaccine recipients in New Zealand without previous COVID-19, with enrichment for Māori, Pacific peoples, older adults ≥ 65 years of age, and those with co-morbidities. Serum samples were analysed at baseline and 28 days after second dose for presence of quantitative anti-S IgG by chemiluminescent microparticle immunoassay and for neutralizing capacity against Wuhan, Beta, Delta, and Omicron BA.1 strains using a surrogate viral neutralisation assay.

Results: 285 adults with median age of 52 years were included. 55% were female, 30% were Māori, 28% were Pacific peoples, and 26% were ≥ 65 years of age. Obesity, cardiac and pulmonary disease and diabetes were more common than in the general population. All participants received 2 doses of BNT162b2 vaccine. At 28 days after second vaccination, 99.6% seroconverted to the vaccine, and anti-S IgG and neutralising antibody levels were high across gender and ethnic groups. IgG and neutralising responses declined with age. Lower responses were associated with age ≥ 75 and diabetes, but not BMI. The ability to neutralise the Omicron BA.1 variant in vitro was severely diminished but maintained against other variants of concern.

Conclusions: Vaccine antibody responses to BNT162b2 were generally robust and consistent with international data in this COVID-19 naïve cohort with representation of key populations at risk for COVID-19 morbidity. Subsequent data on response to boosters, durability of responses and cellular immune responses should be assessed with attention to elderly adults and diabetics.

Keywords: COVID-19; Immunogenicity; Māori; Pacific Islander; Vaccine.

Fig. 1

Participant flow through the study.

Fig. 2

Presence of diabetes by age and ethnicity. Histogram showing bars for each ethnicity within each age grouping (see Ethnicity legend for corresponding colours). Within each bar, opaque colors and corresponding labels indicate the counts for those with diabetes within each group.

Fig. 3

Unadjusted SARS-CoV-2 anti-S IgG responses by age and ethnicity. (A) Unadjusted log₁₀ transformed WHO IU SARS-CoV-2 anti-S IgG responses for participants pre-first vaccination and 28 days post-second vaccination, N = 285. (B) Data shown by age groupings, N = 285. (C) Data shown by major ethnicity categories from New Zealand Census, N = 285. Solid horizontal line represents median and box represents interquartile range. The dotted line represents the log₁₀ transformed value of the cut-off for a positive result (7.1 WHO IU/mL).

Fig. 4

Unadjusted SARS-CoV-2 neutralising antibody responses to ancestral at baseline, and to ancestral and VoCs at 28 days post-vaccination. Unadjusted percent inhibition against ancestral SARS-CoV-2 strain in participants pre-first vaccination (left pane) and inhibition against ancestral, Beta, Delta, and Omicron BA.1 variants from participants 28 days post-second vaccination (right pane), N = 285. Solid horizontal line represents median and box represents interquartile range. Cut-off for positive results is 20%.

Fig. 5

Unadjusted SARS-CoV-2 neutralising antibody responses to ancestral strain at 28 days post-vaccination by age and ethnicity. Unadjusted percent inhibition against ancestral SARS-CoV-2 strain in participants post-second vaccination separated by age groups (left pane) and separated by ethnicity categories (right pane), N = 285. Solid horizontal line represents median and box represents interquartile range.