The opposition on Monday re-ignited an unresolved controversial topic when its presidential candidate Raila Odinga claimed that the government administered tetanus vaccine secretly laced with a hormone said to cause infertility in women.
Mr Odinga claimed that the government deliberately sterilised thousands of women and girls in the guise of tetanus vaccination.
He further claimed that four credible institutions had conducted independent tests on the vaccine, which showed that it had compounds with high amount of anti-pregnancy hormone called human chorionic gonadotropin (hCG) that would render the women and girls sterile.
Mr Odinga said the Catholic Church was right in opposing the jab, which has allegedly 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.
But in a joint statement last evening, the World Health Organization (WHO) and the United Nation Nations Children's Fund (Unicef) expressed "deep" concern on what they said was misinformation in the media on the quality of the Tetanus Toxoid vaccine in the country.
"The allegations are that the tetanus vaccine used by the government of Kenya and UN agencies is contaminated with a hormone (hCG) that can cause miscarriage and render some women sterile.
"These grave allegations are not backed by evidence, and risk negatively impacting national immunisation programmes for children and women," the agencies said in the statement signed by WHO representative in Kenya Dr Custodia Mandihate and Unicef Kenya's acting representative Dr Pirkko Heinonen.
They said the agencies had taken note of test results claiming to show hCG levels in samples submitted to some clinical laboratories, noting that testing for the content of a medicine such as TT vaccine needed to be done "in a suitable" laboratory and from a sample from the actual medicine/vaccine obtained from an unopened pack and not a blood sample.
"Who and Unicef confirm that the vaccines are safe and are procured from a pre-qualified manufacturer," the statement read.
But Mr Odinga said analysis of samples used for the tetanus vaccination from highly regarded institutions on matters of health such as agriQ Quest Limited, Nairobi Hospital Laboratories and the University of Nairobi indicate that it had high contents of beta human hCG that causes infertility.
"Today, we can confirm to the country that the Catholic Church was right.
"Thousands of our girls and women aged between 14 and 49 will not have children because of the State-sponsored sterilisation that was sold to the country as tetanus vaccination," Mr Odinga said.
Addressing the Press at his Capitol Hill office in Upper Hill, Nairobi, Mr Odinga challenged the government to publish the list of all people who took part in the vaccination and apologise to them.
"This was a deliberate action on the part of the government and it should apologise to all those who were vaccinated and explain to them how it intends to reverse the damage," Mr Odinga said.
According to the opposition leader, at least 500,000 women might not be able to bear children based on the vaccination, though he said the figure could even be high as the government has not released the official number of those who were vaccinated.
However, Mr Odinga said all was not lost for those who were vaccinated, saying medical experts have assured them that enforced sterility can be reversed if victims show up for emergency interventions.
Mr Odinga's claims have rekindled a heated debate over the vaccines that the Catholic Church had rejected in 2014 and asked its congregation to boycott the nationwide campaign.
The Church claimed that the vaccine was laced with a hormone said to cause infertility.
But then Health Cabinet Secretary James Macharia disputed the claims and told BBC that the vaccine was safe.
"I would recommend my own daughter and wife to take it because I entirely 100 percent agree with it and have confidence that it has no adverse health effects," Mr Macharia said.
The tangle between the church and the government began on March 2014 when bishops became suspicious about the vaccine, which was targeted at women in the reproductive ages of 14 to 49, and excluded boys and men.
The controversy culminated in the formation of a joint committee of experts from the government and the Church, which was co-chaired by Prof Fredrick Were from the ministry and Dr Stephen Karanja representing the Church.
But months after the joint testing, the company hired to test the samples --Agriq Quest Ltd -- in a damning letter claimed that the ministry through its then Principal Secretary Nicholas Muraguri wanted the results altered.