Consumers should not buy antigen testing kits being sold in supermarkets due to the risk of false results, according to chief medical officer Dr Tony Holohan.
The National Public Health Emergency Team is "genuinely concerned" about the sale of such kits and their use in uncontrolled circumstances, he said.
Their use poses a “real risk” to the pandemic response because of the false reassurance an incorrect negative result could provide.
Supermarket chain Lidl began selling Covid-19 antigen tests in Ireland this week, at a cost of €24.99 for a pack of five.
Antigen tests are faster and cheaper than the PCR tests used by the HSE but they are less accurate, particularly where a person is not showing symptoms.
With a typical test sensitivity of 50 per cent, an antigen test would fail to pick up half the cases at a wedding, for example, thereby giving risk to a potential super-spreader event, Dr Holohan said.
Meanwhile, he advised Leaving Certificate students to “take every measure” to ensure they do not get infected in the run-up to the exam.
He urged candidates to cut their contacts as the exam approaches and suggested the break between the end of classes and the start of exams should be used as a quarantine period.
He also advised third-level students to avoid the temptation of after-exam parties due to the risk of infection.
The reproduction number, a measure of how many other people a case infects, now stands at "at or about one", according to deputy chief medical officer Dr Ronan Glynn.
The incidence of the disease was broadly static over the past week, while hospitalised patients and numbers in ICU continue to fall, he said.
Deaths have been “virtually eliminated” in nursing homes, he pointed out.
No Covid-19 cases were reported among people aged 85 and over on Friday, according to Nphet.
Just two cases were recorded in the 75 to 84-year-old age group due, officials say, to the impact of vaccination. Cases among children and young people have risen slightly.
Counties Donegal, Kildare, Dublin, Roscommon, Louth and Cavan have higher than average incidence and/or higher test positivity.
After several months of stability, the average number of contacts increased last week from 2.6 to 2.8.
A further four deaths of Covid-19 patients were reported by Nphet on Friday. This brings to 4,918 the total number of deaths in the pandemic.
Nphet also reported 434 confirmed cases of the disease, bringing to 251,904 the total number of cases in the Republic.
Of the new cases, 197 were in Dublin, 44 in Cork, 34 in Kildare, 20 in Limerick and Meath, with the remaining 119 cases spread across 16 other counties.
The 14-day incidence of the disease now stands at 130 cases per 100,000 people nationally. Donegal has the highest county incidence, followed by Kildare. Kerry has the lowest incidence.
The median age of cases is 31 years and 80 per cent are under 45.
With further easing of restrictions due on Monday, many more business will open and the economy will begin to restart in earnest, Dr Holohan said.
“It is extremely important that business owners, employees and customers take great care and review safety protocols and practices and ensure to consider all the actions we can all take as individuals to protect ourselves and our loved ones.
“Only return to the workplace if it is necessary to do so. Continue to wear a mask, practice social distancing, good hand hygiene and cough etiquette. If you feel unsafe in a crowded environment feel empowered to turn around and go home.
Twenty cases of the B1617 variant first identified in India have been detected in Ireland, Dr Glynn said.
In addition, there have been 73 cases of the B1351 (South African) variant of concern and 28 cases of P1 (Brazil).
On Friday morning, 126 Covid-19 patients were hospitalised, of which 34 were in ICU. There were 15 additional hospitalisations in the previous 24 hours.
Up to Wednesday, 1,700,538 doses of vaccine had been administered: 1,233,067 people first doses and 467,471 people second doses.