The week-long campaign allowed 844,000 people to receive one dose of the vaccine, which offers protection against the deadly disease for six months, WHO spokesman Tarik Jasarevic told reporters in Geneva.
Northeastern Nigeria is in the grip of a humanitarian crisis caused by the Boko Haram insurgency, which has killed at least 20,000 people and displaced more than 2.6 million.
As of Monday, nearly 4,000 suspected cases of cholera had been detected in the region in just over a month, according to WHO numbers.
Cholera is transmitted through contaminated drinking water and causes acute diarrhoea, with children facing a particularly high risk of infection.
With 54 related deaths so far, the case fatality rate, which measures the severity of an epidemic by defining the proportion of fatal cases within a specific timeframe, is currently at 1.4 percent — well above the emergency threshold of one percent.
The first cholera case was identified in Borno State on August 16 and has since spread, mainly in camps for those displaced by the Boko Haram insurgency.
Two doses of the vaccine are needed to offer full protection, but in emergency situations, the WHO allows for a single dose to be given to speed up the coverage.
Water-borne diseases are a constant threat because of a lack of adequate sanitation as well as stagnant groundwater during the current rainy season.
In addition to the vaccination campaign, WHO and other aid organisations are helping the Nigerian government to respond to the outbreak by establishing cholera treatment centres, “increasing outreach to communities with information on cholera and on prevention”, Jasarevic said.
Providing access to safe water was also a priority, he said.
About 8.5 million people in Nigeria’s northeast, out of 17 million in the wider Lake Chad region encompassing Nigeria, Cameroon, Chad and Niger, need humanitarian assistance, according to the United Nations.
Widespread malnutrition and the severe hygiene crisis in northeastern Nigeria, aggravated by the current rainy season and the limited access to clean water, especially in remote areas and in the overcrowded camps, have sparked growing fears that the cholera epidemic could spread across the region.