Vaccines from different manufacturers should not be combined, doctors in the UAE said in response to UK trials giving people two different jabs in exceptional circumstances.
A mix-and-match approach has been considered in the UK to help manage limited supplies and reach as many people as possible with the Pfizer/BioNTech vaccine and the alternative Oxford/AstraZenica jab.
That approach has been rejected in the UAE, where doctors only have access to the Chinese made Sinopharm and Pfizer vaccines, each different in their construction.
“The recommendation is to give two doses of the same vaccine,” said Dr Dirar Abdallah, consultant and chairman of internal medicine at Prime Hospital.
“If someone takes a first dose of Sinopharm, Pfizer, AstraZenica or Moderna - it should be followed by the same vaccine.
“There have been some controversies after the UK announced it would allow the mixing of vaccines in exceptional circumstances.
“Scientists in the US and elsewhere did not agree, but the UK later clarified it would only be done in exceptional circumstances when the second dose of the same vaccine was not available.”
The Pfizer/BioNTech vaccine, given as two doses a few weeks apart, offers up to 95 per cent protection against the virus.
Researchers in the UK wanted to explore whether the immune response can be strengthened further and made more durable with a "heterologous boost" approach by mixing different vaccines.
While the Oxford/AstraZeneca vaccine works in a slightly different way to the Pfizer jab, doctors said it could make a good companion for pairing.
The Pfizer vaccine uses a small amount of genetic code from Covid-19 to teach the body how to ward off infection, while the Oxford alternative is a genetically modified virus altered to not cause infection.
The Oxford vaccine does, however, carry crucial information on how the body can fight off the pandemic virus.
Scientists said the process could bolster the immune system by producing responses in antibodies and T-cells, the body’s natural armoury against disease.
UK authorities have since stated mixing vaccines would only be done in exceptional circumstances.
“We do not recommend to mix the vaccines in the UAE either,” said Dr Abdallah, who also advised people to wait a month after taking a flu jab before having a Covid-19 vaccine.
“Both Pfizer and AstraZenica vaccines are made with the same mechanism, so there is an assumption they could complement each other.
“This does not apply here in the UAE as the Pfizer and Sinopharm vaccines are constructed with very different mechanisms, either by using a spike protein or an inactive virus.
“Because of this we do not recommend to mix vaccines at all here.”
Experts from the World Health Organisation recommended intervals between Pfizer-BioNTech vaccinations could be extended by up to six weeks, to help ease logistical issues.
WHO said the “pragmatic approach” could be considered as a response to “exceptional epidemiological circumstances.”
It said countries seeking to extend the interval should make sure that vaccinated patients still have access to a second dose.
“WHO’s recommendation at present is that the interval between doses may be extended up to 42 days (6 weeks), on the basis of currently available clinical trial data,” it said.
“Should additional data become available on longer intervals between doses, revision of this recommendation will be considered.”
WHO also said no data is available yet on the interchangeability of the Pfizer-BioNTech vaccine with other COVID-19 vaccines. It also cited a lack of evidence about whether vaccination reduces the risk of transmission of the virus to other people.
Elsewhere, health officials said a lack of research into multiple vaccines and their efficacy prevented the same UK advice being adopted in the UAE.
“Covid-19 vaccines are new and limited in number, subsequently there are no studies to shed light on the results of taking different vaccines,” said Dr Adil Sajwani, a family medicine specialist at the Ministry of Health and Prevention and member of the national awareness team for Covid-19.
“In theory, one can take different vaccines, we have been doing that against flu, measles, hepatitis B and other illnesses.
“But as coronavirus is a new disease and its vaccines have just been announced, it’s advisable people avoid mixing vaccines until we have done clinical trials.”
