The World Health Organization, the United Nations' health agency, has declared Sierra Leone to be free of deadly Ebola.

WHO made the announcement following 42 days without a single diagnosed case of the disease, and crowds took to the streets of the capital Freetown to celebrate.

That period of time represents two 21-day incubations periods for the deadly virus.

The country will conduct 90 days of additional monitoring to ensure early detection of any new cases of the disease, the Geneva-based organizations said.

Since the Ebola outbreak began last year, more than 11,300 people have died in Sierra Leone, Guinea and Liberia, the countries hardest hit by the virus.

Among the nearly 4,000 who died in Sierra Leone were more than 220 health workers as they battled the disease in that country.

In Freetown, a candlelight vigil was held in their memory.

"They died so we could live," said university student Fatmata, who was taking part in the tribute ceremony broadcast on radio and television stations across the country.

Sierra Leone is the second country to be declared Ebola-free, after WHO made a similar announcement about Liberia in September.

A handful of cases still remain in Guinea, the country where the outbreak began in late 2013.

WHO says seven new cases there have been recorded there in the past 3 weeks.

The declaration of Sierra Leone's Ebola-free status was welcome news there, said Dr. Oliver Johnson from King's College London, who worked at an Ebola clinic in Freetown.

"[For] everyone I've spoken to, there's a sense of relief that this might finally be over and maybe a bit of disbelief that after so many false starts, or false ends, we might finally be there," he said.

WHO would support Sierra Leone during the next 90-day monitoring period, officials said.

"We now have a unique opportunity to support Sierra Leone to build a strong and resilient public health system ready to detect and respond to the next outbreak of disease or any other public health threat," said WHO representative Anders Nordstrom, attending the Freetown ceremonies.

The celebrations were bittersweet, Sierra Leone officials acknowledged.

"It's kind of like a mixed emotion," said Tunis Yahya of the country's National Ebola Response Center. "People are happy, but also many are depressed because they lost their families."