The World Health Organization declared Liberia Ebola-free on Saturday, after 42 days without a case of the disease, twice the incubation period of the deadly virus that killed more than 4,000 people in the West African country and more than 11,000 people across West Africa over the last year.

While Liberians and aid agencies working there let out a collective sigh of relief Saturday, the country is not out of the woods just yet. With a more than 1,300-mile border with Sierra Leone and Guinea, two nations where Ebola cases continue to be reported, Liberia must remain vigilant, WHO said in a statement.

Persistent outbreaks in Sierra Leone and Guinea create “a high risk that infected people may cross into Liberia over the region’s exceptionally porous borders,” the statement said. The WHO also advised it would maintain “an enhanced staff presence in Liberia until the end of the year as the response transitions from outbreak control, to vigilance for imported cases, to the recovery of essential health services.”

As Liberian authorities threw all of the country’s fledgling medical system at the nightmarish Ebola virus, little in terms of resources were left to address Liberia’s other potentially devastating health threats like measles and polio. The United Nations announced Friday that it would be joining with local authorities to conduct large-scale immunization campaigns as Ebola was gradually stamped out there. Led by the UN, local authorities and international aid groups hope to vaccinate 683,000 children at risk of infection.

Doctors Without Borders -- often shortened to MSF as an initialism of its French translation Médecins Sans Frontières -- also urged caution over the situation in Liberia and called for “health needs to be addressed as a priority” there. MSF was one of the first organizations to commit resources to fight the outbreak in March of last year. The aid group repeatedly sounded the alarm about the impending crisis, which it called out of control last summer. While the international community was crucial to eradicating Ebola in Liberia, the sluggish and underwhelming response of far more capable countries leaves sobering questions about the priorities of the international community and its willingness to act quickly.

“Quite simply, we were all too late,” said Henry Gray, MSF’s head of Ebola operations,  in a statement on Saturday. “The world - including MSF - was slow to start the response from the beginning. That lesson has been learned, at the cost of thousands of lives, and we can only hope it will prevent the same thing happening again in the future.”

Every one of Liberia’s 15 counties reported cases of Ebola over the course of the more than year-long crisis. Many experts worried that Ebola would become a permanent health threat in West Africa, where it had never struck before last year. More than 375 health workers died in Liberia alone during the outbreak. The last reported case of Ebola in Liberia was a woman in the greater Monrovia area who became sick on March 20 and died one week later, according to WHO.