The World Health Organisation has advised against mixing of Covid-19 vaccines as there is no scientific evidence to support the same.

The global health agency has instead termed it ‘chaotic’ adding that the final decision on mix and match should be left to health experts as the safety and efficacy of a “mixed-dose” vaccination series hasn’t been established.

This comes as some countries decided to give different second doses in the wake of vaccine shortages and supply chain challenges, especially for AstraZeneca.

“It is a little bit of a dangerous trend here. It will be a chaotic situation in countries if citizens start deciding when and who will be taking a second, a third and a fourth dose,” Chief Scientist at the WHO Soumya Swaminathan said.

“Data from mix and match studies of different vaccines are awaited – immunogenicity and safety both need to be evaluated.”

Kenya is among countries that have been hit by vaccine shortage after the Indian government halted vaccine exports due to satisfy domestic demand.

But the Health ministry is yet to decide whether mixing vaccines from different manufacturers will be the next viable option.

“Data is emerging but then this is still work in the pipeline. In some countries like Spain and Germany, those who received their first dose of Pfizer vaccine or AstraZeneca have gotten the reverse,” Health DG Dr Patrick Amoth said.

“Data will emerge from that particular platform to be able to advise us and that is why it is also important for us to be able to get other vaccines so that we can be able to try on those in our own local setting.”

The ministry has halted the issuance of the first dose of the AZ vaccine with all those doses coming in expected to be directed towards the administration of the second jab.

The government expects 1.7 million doses of Pfizer vaccine from the US government from the 14 million the US has pledged to donate to the African states.

The Pfizer and Johnson and Johnson are to be given to Kenyans who are yet to receive a single shot in an effort for the country to attain herd immunity.

An earlier study by Oxford University on mixing Pfizer and AZ vaccines had shown that receiving the two vaccines as first and second dose induced higher antibodies.

Another similar study by Saarland University in Germany had also shown a stronger immune response in patients who received AZ jab followed by Pfizer than they did in patients who had received two doses of the AstraZeneca vaccine.

The two studies are yet to go through the peer-review process where independent scientists will have to evaluate them before making the final decision.

Data from the ministry shows that by Saturday, a total of 1,618,356 vaccines had so far been administered across the country with 581,003 people having received their second dose.

This means the proportion of the adult population fully vaccinated stands at 2.1 per cent.

Another 1,037,353 have received their first dose with the uptake of the second dose among those who received their first dose being at 56 per cent.

In terms of uptake of vaccines per the priority groups, 106,100 are healthcare workers, 81,578 are teachers, 46,214 are security officers, 181,225 are people aged 58 years and above while 165,874 are members of the public.