The Health ministry has dismissed claims that a tetanus vaccine given to women of reproductive age was secretly laced with a hormone said to cause infertility.
At the same time, the United Nations agencies World Health Organization and Unicef said the vaccine is safe for use.
Speaking to the Nation on Tuesday, UN resident coordinator Siddharth Chatterjee reiterated that the vaccines procured by WHO in partnership with Unicef are fit for use.
"This is the same vaccine used across 52 other countries, including India, where the prequalified manufacturer is based," he said, adding that the two organisations only procure the vaccines upon request from the ministry.
Between May and June, the two organisations bought an estimated three million doses of tetanus toxoid meant for an upcoming immunisation campaign whose date is yet to be announced.
"Our intention is to preserve the lives of mothers and children. It is about protecting the lives of people, mothers and children. Vaccines work," Mr Chatterjee said.
Health Cabinet Secretary Cleopa Mailu on Tuesday described the controversy as an old matter.
He said the issue had already been resolved through a joint tetanus vaccine testing committee that comprised Health ministry officials, academia and representatives of the Kenya Conference of Catholic Bishops (KCCB).
Dr Mailu said the opposition's statement on Monday was a baseless pronouncement that was not backed by any scientific evidence, adding that it was intended to cause fear and despondency among Kenyans.
"The joint committee found the sampled vaccine vials safe and free from any contaminants and recommended the vaccine for use," Dr Mailu said in a statement.
"Subsequent consultative meetings between the ministry and KCCB gave a clean bill of health to the tetanus vaccine with successful vaccination campaigns taking place in 2016 and 2017," he added.
Nasa leader Raila Odinga had claimed that the vaccine was secretly laced with a hormone that caused infertility in women between 14 and 49 years.
"Tests results in our possession indicate that some of the women who got this vaccination have since sought further tests and obtained results indicating that they can never carry a pregnancy unless a process of reversing the effects is initiated," he said.
It is estimated that Kenya loses one child every day due to neonatal tetanus, translating to nearly 20 newborns per 1,000 live births, with 370 of them dying every year.
Despite this, the country is yet to achieve the required global maternal and neonatal tetanus (MNT) elimination targets of 69 percent, and hence the routine immunisation drives.
"In an endeavour to achieve MNT elimination status, Kenya previously conducted mass vaccination campaigns in 2003, 2006 and 2009," Dr Mailu said.
Kenya initiated its MNT elimination programme in 2013 mostly targeting 11 counties -- Kilifi, Mombasa, Meru, Mandera, Wajir, Garissa, Baringo, West Pokot, Turkana, Samburu and Narok.
These were considered high-risk areas where women are likely to contract tetanus and transmit it to unborn babies.
The mapping of these devolved units, Dr Mailu explained, was based on a joint assessment carried out in 2012 by the ministry, WHO, Unicef and other health stakeholders.
The assessment identified 60 districts (currently sub-counties) in 16 counties at risk of MNT, which is usually transmitted from mother to child.