Unvaccinated people who were infected months earlier are five times more likely to contract Covid-19 than people who have been fully vaccinated and have no previous infection, it follows from data provided today by that US health authority.

"These data show, with great emphasis, that vaccines provide greater protection against the symptomatic forms of Covid-19," said infectious disease physician Mike Saag of the University of Alabama at Birmingham, who was not involved in the study. .

The survey analysed data from nearly 190 hospitals in nine states and researchers looked at nearly 7,000 adult patients who were hospitalised this year with respiratory illnesses or Covid-19-like symptoms.

About 6,000 of these patients were fully vaccinated with Moderna or Pfizer injections between three and six months before hospital admission, while another 1,000 were unvaccinated but had been infected with Covid-19 in the same time period.

About 5% of vaccinated patients tested positive for SARS-CoV-2, compared to about 9% of patients in the unvaccinated group.

The researchers also considered other data, such as age and the intensity of virus circulation in different areas to conclude that the unvaccinated group was at a higher risk of contracting the disease.

The study supports some previous research, including research that found higher levels of antibodies in vaccinated patients than in others who had contracted the disease.

Also according to the researchers, not enough data were collected to reach any kind of conclusion about the Johnson & Johnson vaccines.