The number allowed to meet outdoors and indoors has been slashed as renewed pandemic restrictions were imposed in Northern Ireland.
The country has one of the highest rates of spread in the UK and the most recent reproductive estimate for coronavirus is 1.3.
Totals socialising indoors at households will be reduced to six from no more than two households after Stormont ministers met on Thursday to rubber stamp the change.
The limit on those attending outdoor gatherings will fall from 30 to 15.
He added: “Unless we take action now I fear it would soon have been too late to arrest further extensive spread of the virus.”
A meat plant in Co Antrim is to close for a deep clean following a coronavirus outbreak, Mr Swann said.
Cranswick Country Foods in Cullybackey processes pigs.
Mr Swann told a press conference at Stormont that at least 35 cases have been identified associated with the factory.
He added: “All the workers and recent visitors to the factory should be required to self-isolate.”
Another 51 people in Northern Ireland have tested positive for coronavirus, according to the Department of Health on Thursday.
Certain events can have more than 15 people attending as long as a risk assessment is carried out and necessary measures are put in place.
A Stormont executive statement said: “This will include weddings, church services and sporting events where a close adherence to social distancing and hygiene regimes continues to apply.”
The executive also agreed some upper limits on gatherings and events that can be introduced quickly depending on the transmission of the disease.
The changes will be introduced next week.
The changes will apply across Northern Ireland but ministers accepted that localised measures may be needed in the future to arrest the spread of the virus.
The executive agreed that no new indicative dates for more easing will be set and no further restrictions lifted.
He said that partly explained why a similar increase in hospital admissions had not yet been seen.
The medic said some of the evidence about people’s behaviour was anecdotal.
“We are seeing increased social mixing, close contact occurring in domestic settings.
“What we now need to do is act on that evidence and act on it in a proportionate way.”
He backed the Stormont Executive’s decisions around restrictions.
“I believe they send a signal to the community as a whole.
“They reflect all our concerns at the growing numbers of Covid-19 cases.”
Mr Swann attacked “armchair experts” who believed they knew better and had decided to ignore official advice.
One person has been arrested and is in police custody over “personal abuse” directed at the minister, he confirmed.
Meanwhile, from this Saturday those arriving in Northern Ireland from Portugal will not need to self-isolate, Mr Swann said.
Austria, Croatia and Trinidad and Tobago will be added to countries for which quarantine is required.