Longer interval between the two doses of the Pfizer-BioNTech Covid vaccine in persons who did not have a previous infection resulted in more than 9-folds increase in antibody titers, according to a new analysis of data from the SIREN (SARS-CoV-2 Immunity and Reinfection Evaluation) trial.¹ These findings were presented at the 32nd European Congress of Clinical Microbiology & Infectious Diseases.

In this trial, serum anti-spike binding antibody levels were measured in 5871 health care workers from the UK who had received the Pfizer-BioNTech vaccine. Of these, 1882 had been fully vaccinated with two doses at least 14 days before the start of the study, while 3989 had received only the first dose at least 21 days earlier. Majority of the participants were women (82.3%).

The geometric mean titers of anti-spike antibodies were 75.48 binding antibody units/mL among Covid-naïve participants after the first dose. Their antibody levels rose to 7050 BAU/mL following the second dose demonstrating seroconversion. The anti-S antibody levels were higher after the first dose in those who had earlier had natural SARS-CoV-2 infection. The antibody titers were 2111.08 BAU/mL after one dose, but 6052.39 BAU/mL after the second dose, less than in the infection naïve group.

A longer gap between the infection and vaccination led to higher antibody levels; at 3 months, the antibody levels were 1970.83 BAU/ml, while the levels were 13,759.31 BAU/ml 9 months after the infection. Similarly, extending the interval between the doses in participants who had not had Covid infection also saw elevated antibody titers; a gap of more than 10 weeks resulted in more than 9-folds increase in antibody titers, from 1268.72 with 2-4 weeks interval after the first dose to 11,479.73 BAU/ml.

This study shows that longer interval between the two doses of Covid-19 vaccine led to higher antibody levels in infection-naïve individuals and provides evidence-based support to increasing the interval from the 3-4 weeks gap that was earlier recommended resulting in better immunity.

References

1. Otter AD, et al. Abstract 03757. Presented at: European Congress of Clinical Microbiology and Infectious Diseases; April 23-26, 2022; Lisbon, Portugal (hybrid meeting).
2. https://www.healio.com/news/infectious-disease/20220425/longer-intervals-between-covid19-vaccine-doses-produces-higher-antibody-levels