A study carried out on the rate of Covid-19 infection in the Irish population has estimated that three times more people between 12 and 69 were infected with the virus than were officially detected.

The study, which was conducted by the Health Protection Surveillance Centre and the National Virus Reference Laboratory, found that less than 2 in every 100 people have been infected with the virus.

The study, the first of its type in Ireland, measured antibodies to SARS-CoV-2 virus, which are an indication of past infection with Covid-19.

Blood tests were taken from a random sample of 1,733 people aged 12 to 69 years in Dublin and Sligo in June and July.

It reported that a prevalence of infection of 0.6% in Sligo and 3.1% in Dublin. The HPSC said it was then able to estimate that the national prevalence rate was 1.7%.

It said that using data from the study it "estimates that that 59,500 people in Ireland in the age group 12 to 69 years had been infected with SARS-CoV-2 up to mid-July".

It said this was three times more than that detected through the surveillance of notified cases.

The HSE said that 33 samples from 1,733 tested positive for antibodies, with 28 in Dublin and five in Sligo.

In a statement, it said: "Of those who were found to have antibodies, 73% had symptoms that are included in the Irish Covid-19 case definition; that is, one or more of the following: fever, cough, shortness of breath, loss of sense of taste or loss of sense of smell.

"One third of all those who were found to have antibodies reported loss of sense of smell and/or taste."

Principal investigator for the HPSC Dr Derval Igoe, said: "It is not surprising that a relatively low national seroprevalence of 1.7% was observed here.

"Other countries in Europe, such as Spain and Italy, where there has been a much more intense epidemic, have reported national seroprevalence estimates of 5% and 2.5% respectively.

"This means that the vast majority of people living in Ireland had not been infected with SARS-CoV-2 virus by the time of the study.

"As a society, we need to continue with our public health measures, including physical distancing, respiratory etiquette, hand hygiene and the use of face coverings, until a vaccine for Covid-19 is available."

Acting Chief Medical Officer Dr Ronan Glynn said: "The low prevalence rate indicates that the measures put in place early, as well as the sensitive case surveillance, testing and contract tracing system, have been effective in minimising community transmission."

Director of the HPSC Dr John Cuddihy added: "According to the World Health Organization (WHO), 80% of all Covid-19 infections are mild or asymptomatic, so some of these cases are unlikely to be detected. 

"Furthermore, not all symptomatic people will seek health care or have a Covid-19 diagnostic PCR test.

"Therefore, underestimation of cases of Covid -19 highlights the importance of seroprevalence studies as a complement to case-based surveillance.

"We will be repeating studies on the prevalence of Covid-19 infection over the next year to help us understand how Covid-19 is spreading within the community in Ireland."