LONDON — The World Health Organization says smoking is linked to a higher risk of severe illness and death from the coronavirus in hospitalized patients, although it was unable to specify exactly how much greater those risks might be.

In a scientific brief published this week, the U.N. health agency reviewed 34 published studies on the association between smoking and COVID-19, including the probability of infection, hospitalization, severity of disease and death.

WHO noted that smokers represent up to 18% of hospitalized coronavirus patients and that there appeared to be a significant link between whether or not patients smoked and the severity of disease they suffered, the type of hospital interventions required and patients’ risk of dying.

In April, French researchers released a small study suggesting smokers were at less risk of catching COVID-19 and planned to test nicotine patches on patients and health workers — but their findings were questioned by many scientists at the time who cited the lack of definitive data.

WHO says “the available evidence suggests that smoking is associated with increased severity of disease and death in hospitalized COVID-19 patients. It recommends that smokers quit.