People who received Johnson & Johnson's Covid-19 vaccine may benefit from a booster dose of Pfizer or Moderna, preliminary results of a US study showed.

The study, funded by the National Institutes of Health (NIH), was eagerly awaited in the United States because it looked at the possibility of “mixing” vaccines — using a different vaccine than the initial doses for the booster shot — which is not currently allowed in the country.

For people originally inoculated with J&J, antibody levels were four times higher after a J&J booster, 35 times higher after a Pfizer booster and 76 times higher after a Moderna booster.

Additionally, “no safety concerns were identified” after booster doses were administered, it found, according to a Reuters report.