The Health Information and Quality Authority has published a review of the international literature on long Covid.
It said that long Covid is a complex condition, involving a wide range of symptoms that can be debilitating and vary significantly from person to person.
The most common symptoms include fatigue, brain fog, memory loss and or confusion, a loss of smell and shortness of breath.
Although many people will experience an improvement in symptoms over time, for some long Covid can be long-lasting.
HIQA's review included 51 primary research studies, which examined over 1.1 million participants, and four international registry documents.
In studies based on self-reported data, estimates for the prevalence of long Covid in the general population ranged from 15% to 53%.
It said that much of this variation may be due to differences in reporting methods and population demographics within studies.
While prevalence estimates were highest in those with a history of severe Covid-19 illness, long Covid was reported across all populations and age groups.
Michelle O’Neill, Deputy Director of Health Technology Assessment at HIQA, said there is still a lot to learn about long Covid.
The review of international literature found that those with long Covid are more likely to be women, to be older, and to have been admitted to hospital because of Covid-19.
She said it is not known why long Covid occurs.
Ms O'Neill said that for those who have had Covid-19, some people may experience worsening of a pre-existing condition, while some experience new symptoms or conditions, or experience symptoms that continue long after the initial infection has ended.
The research found that long Covid can result in sustained, significant reductions in quality of life and functioning in some individuals and a substantial burden on healthcare systems.
Resourcing of existing services, as well as ensuring the availability of multidisciplinary long Covid services, would help provide appropriate care to those experiencing long Covid.
The HSE has eight post-acute clinics, which treat patients up to 12 weeks after a Covid-19 infection.
It also said it has six long Covid clinics for longer term issues.