Antibodies study shows vast majority of public unlikely to have been infected with Covid-19

Ireland appears to be a long way off from reaching ‘herd immunity’ from coronavirus after a new study indicated the vast majority of people were unlikely to have been infected with it.

The results in the first study of its kind in measuring antibodies for the virus, which are an indication of being infected in the past with Covid-19, was published today.

The main aim was to find out how widely coronavirus has spread in Ireland and what age groups were affected.

The study reported a prevalence of infection of just 0.6pc in Sligo and 3.1pc in Dublin.

Based on these results, the Health Protection Surveillance Centre (HPSC) estimated the proportion of people between 12 and 69 years of age with coronavirus antibodies among the population living in Ireland was 1.7pc.

A representative sample of 1,733 people aged between 12 and 69 years of age in both Sligo and Dublin participated in the study carried out by HPSC and the National Virus Reference Laboratory (NVRL) in June and July this year.

Of the 1,733 samples tested, 33 tested positive for antibodies. Twenty-eight of these were in Dublin, and five in Sligo.

No statistical differences were identified in the prevalence by age group, or between males and females.

Of those who were found to have antibodies, 73pc had symptoms that included 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 or taste.

Dr Derval Igoe, Principal Investigator for the Study to Investigate COVID-19 Infection in People Living in Ireland (SCOPI) at the HPSC said: “It is not surprising that a relatively low national seroprevalence of 1.7pc 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 5pc and 2.5pc respectively.

She said this means that the vast majority of people living in Ireland had not been infected with coronavirus 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.”

Using the prevalence data from this study, the HPSC estimates that that 59,500 people in Ireland in the age group 12 to 69 years had been infected with Covid-19 up to mid-July; three times more than that detected via surveillance of notified cases.

Dr Ronan Glynn, Acting Chief Medical Officer added: “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.”

Dr John Cuddihy, Director of the HPSC, added: “According to the World Health Organization (WHO), 80pc 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.”

“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.”

The presence of COVID-19 antibodies in a blood sample is a sign that a participant was infected with the COVID-19 virus at some time in the past.

Experts say currently, there is not enough evidence to be sure if antibodies to COVID-19 will protect people from getting sick with COVID-19 again.

Further evidence is required to understand how long the antibodies last and what level of antibodies is necessary to confer immunity. Researchers say this is why it is very important that everyone continues to follow all the social distancing and hygiene measures recommended by the government regardless of their antibody test result.