The effectiveness of Pfizer’s COVID-19 vaccine at protecting against hospitalisation appears to be robust for at least five months, a major study suggests.

But protection from acquiring the infection wanes over time regardless of the variant, the data show.

The study, funded and co-written by Pfizer, also showed the vaccine was no less effective against the Delta variant compared with other variants of SARS-CoV-2.

However, it added to a growing debate on whether Australia should start administering booster shots, especially to doctors and others who were vaccinated in the first half of 2021.