Protective antibodies and T cell responses to Omicron variant after the booster dose of BNT162b2 vaccine

The high number of mutations in the Omicron variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes its immune escape. We report a longitudinal analysis of 111 vaccinated individuals for their antibody levels up to 6 months after the third dose of the BNT162b2 vaccine. After the third dose, the antibody levels decline but less than after the second dose. The booster dose remarkably increases the serum ability to block wild-type or Omicron variant spike protein’s receptor-binding domain (RBD) interaction with the angiotensin-converting enzyme 2 (ACE2) receptor, and these protective antibodies persist 3 months later. Three months after the booster dose, memory CD4⁺ and CD8⁺ T cells to the wild-type and Omicron variant are detectable in the majority of vaccinated individuals. Our data show that the third dose restores the high levels of blocking antibodies and enhances T cell responses to Omicron.

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After the third BNT162b2 dose, the antibody levels decline slower than after the second

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The protective antibodies persist for at least 3 months after the third dose

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81% of individuals have T cell responses to Omicron at 3 months after third dose

Dynamics of antibody response to BNT162b2 vaccine after six months: a longitudinal prospective study

BACKGROUND

SARS-CoV-2 mRNA vaccines have proven high efficacy, however, limited data exists on the duration of immune responses and their relation to age and side effects.

METHODS

We studied the antibody and memory T cell responses after the two-dose BNT162b2 vaccine in 122 volunteers up to 6 months and correlated the findings with age and side effects.

FINDINGS

We found a robust antibody response to Spike protein after the second dose. However, the antibody levels declined at 12 weeks and 6 months post-vaccination, indicating a waning of the immune response over time. At 6 months after the second dose, the Spike antibody levels were similar to the levels in persons vaccinated with one dose or in COVID-19 convalescent individuals. The antibodies efficiently blocked ACE2 receptor binding to SARS-CoV-2 Spike protein of five variants of concern at one week but this was decreased at three months. 87% of individuals developed Spike-specific memory T cell responses, which were lower in individuals with increased proportions of immunosenescent CD8+ TEMRA cells. We found antibody response to correlate negatively with age and positively with the total score of vaccination side effects.

INTERPRETATION

The mRNA vaccine induces a strong antibody response to SARS-CoV-2 and five VOCs at 1 week post-vaccination that decreases thereafter. T cell responses, although detectable in the majority, were lower in individuals with higher T cell immunosenescence. The deterioration of vaccine response suggests the need to monitor for the potential booster vaccination.