Less than 2% of people in Ireland have antibodies to the SARS-CoV-2 virus, which is an indication of past infection with COVID-19, a new study has found.

In June, the HSE announced a new study, which aimed to provide an overall estimate of how many people in Ireland have been infected with COVID-19.

The Study to Investigate COVID-19 Infection in People Living in Ireland (SCOPI) measured exposure to the virus using an antibody blood test, and people from Dublin and Sligo were invited to attend.

These two counties were selected as sample locations because they represented areas of the country with higher and lower known levels of infection respectively. Therefore using a representative sample from each of these counties would provide an overall national estimate of infection within the Irish population.

The study was carried out by the Health Protection Surveillance Centre (HPSC) and the National Virus Reference Laboratory (NVRL) and a representative sample of 1,733 people aged between 12 and 69 took part in June and July.

Among them, 33 tested positive for antibodies - 28 in Dublin and five in Sligo.

This is a prevalence of infection of 0.6% in Sligo and 3.1% in Dublin. Based on these results, the HPSC estimates a national prevalence rate of 1.7%.

Of those who were found to have antibodies, 73% experienced symptoms that are included in the Irish COVID-19 case definition, which 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.

According to SCOPI's principal investigator at the HPSC, Dr Derval Igoe, 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," she noted.

Using the prevalence data from this study, the HPSC estimates that 59,500 people aged between 12 and 69 had been infected with SARS-CoV-2 up to the middle of July. This is three times more than that detected via surveillance of notified cases.

"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," commented Dr Ronan Glynn, acting chief medical officer.

Dr John Cuddihy, director of the HPSC, pointed out that 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 healthcare 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," he said.

"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," he added.