A new preprint study has shown a decline in antibody levels 7 months after taking the Pfizer-BioNTech vaccine.^1.2 The study included 46 healthy young or middle-aged adults, who had been fully vaccinated with the Pfizer-BioNTech vaccine. T cell responses and antibody responses to the homologous Wu strain as well as several variants of concern, including the Mu (B.1.621) variant were analysed 6 months (day 210 post-primary vaccination) after the second dose.

A 7.3-fold decrease in anti-spike binding IgG response was observed in all study participants between one month and six months after the second dose of the vaccine. The male participants recorded a higher decline compared to the female participants; 9.1-fold vs 6.3-fold, respectively. However, this difference was non-significant. Compared to the titers at 3 weeks, the live virus neutralization antibody titers against the homologous USA-WA1/2020 strain reduced 7-folds at 6 months. The decrease in male participants was 7.4-folds and 6.6-folds in female participants. Measurement of T cell responses showed significant downregulation of spike-specific CD4 T cells expressing IFN-g and TNF on day 210 (~6.9 months) compared to day 28 (~1month).

The declining efficacy of Covid-19 vaccines has been reported in several recent studies. Emergence of new variants of concern that show immune escape have also led to concerns about the duration of protection offered by the vaccines. This has generated a global debate on booster dose and countries like the US, Israel, Germany have already started administering the booster shots. The European Medicines Agency (EMA) is the latest to approve booster shots of the Pfizer-BioNTech Covid-19 vaccine for persons aged 18 years and older at least 6 months after the second dose

This study has demonstrated the declining antibody response around 6-7 months after the second dose of the Pfizer vaccine. And, it adds weight to the debate around the booster dose. The study authors have also suggested that “administering a booster dose at around 6 to 7 months following the initial immunization will likely enhance protection”.

References

1. Mehul S. Suthar, et al. Durability of immune responses to the BNT162b2 mRNA vaccine. bioRxiv, September 30, 2021, doi: https://doi.org/10.1101/2021.09.30.462488.
2. Pfizer COVID vaccine antibodies may disappear in 7 months, study says - Medscape - Oct 04, 2021.