A booster dose of Johnson & Johnson's COVID-19 vaccine appears to produce a robust increase in antibodies, according to interim data from two small, early-stage trials, the company said on Wednesday.

"Johnson & Johnson COVID-19 vaccine booster, after single dose primary regimen, provided rapid and robust increase in spike-binding antibodies," the company said.

Significant increases in binding antibody responses were observed in participants between ages 18 and 55, and in those 65 years and older who received a lower booster dose.

The study summaries were submitted to medRxiv on August 24.

The US is set to roll out a booster campaign from September and J&J has been under pressure to produce evidence of whether a booster shot would increase protection from its vaccine.

“We look forward to discussing with public health officials a potential strategy for our Johnson & Johnson COVID-19 vaccine, boosting eight months or longer after the primary single-dose vaccination," said Mathai Mammen, M.D., Ph.D., Global Head, Janssen Research & Development, Johnson & Johnson.

The news comes as several countries, including the US, have started offering booster doses of other vaccines to vulnerable individuals, including the immunocompromised, as the Delta variant surges.