So far no regulatory agency of medications in the world has approved a combination of doses
Cases of thrombosis linked to AstraZeneca-Oxford vaccine have led Germany to announce that the vaccination guidelines of the citizens who received a first dose of this manufacturer will be completed with vaccines from other laboratories. This decision has opened the debate about the possibility to follow the same strategy to advance in the immunisation of populations. Although so far no regulatory agency of medications in the world has approved a combination of doses because there are no available data supporting its efficacy and safety and, consequently, it is indicated that the vaccination guideline must be completed with doses from the same pharmaceutical company, the first studies point into the direction that this is effective.
The race to achieve immunisation against covid-19 through vaccines and the difficulties experienced by many countries to receive them have made some people wondering if they can be vaccinated with doses from different manufacturers. No drug regulatory agency in the world has approved a combination of doses in the absence of data to support its efficacy and safety, so health authorities indicate that the vaccination schedule must be completed with doses from the same pharmaceutical company.
Except Janssen’s, designed to be injected in a single dose, all other approved vaccines in the world consist of two doses given at times set by the manufacturer. There are currently two ongoing clinical trials studying the safety and efficacy of mixing vaccines: the first one investigates the combination between AstraZeneca-Oxford and Pfizer/BioNTech and the second one the combination between AstraZeneca-Oxford and Sputnik V. If results were positive, which publication is expected by the end of this year, the world vaccination program could be speeded up.
The Centers for Disease Control and Prevention (CDC) from the United States currently highlight that “the vaccines are not exchangeable”. The European Medicines Agency (EMA) has explained to Verificat in an email that “the enterprises involved in the development of these vaccines have not reported any proof endorsing the mixing of vaccines”. The UK Department of Health positions in the same line, considering that “every effort should be made to give [patients] the same vaccine”.
"What is important is the first dose"
Pending data supporting combined guidelines, Mary Ramsay, head of immunisations at Public Health England, explained to the specialised journal British Medical Journal that doses from different manufacturers can be given if vials of the same brand are not available or if it is not known which vaccine a person received as a first dose. The spanish physician, Oriol Mitjà, researcher at hospital Germans Trias i Pujol, specialised in infectious diseases, has explained to Verificat that, despite no data are available, in case that the reception of the second dose was compromised “what is important is the first dose”, due to the immunisation degree it provides. If a combined guideline were to be applied without being authorised, he says that “the technology [of the vaccines] is irrelevant” because “what is important is the particle that they carry as a vehicle” to trigger the immune response of the organism”. That is, in his opinion, one dose with mRNA and another viral vector can be given, although he outlines that the regulatory course must be followed and vaccination strategies must be fulfilled.
The UK government has opted to delay the administration of the second dose for up to 12 weeks. The goal is that the larger number of citizens receive the first dose achieving a sufficient degree of immunity to drastically reduce contagions, deaths and hospitalisations. This strategy, together with strong restrictive measures, have made the epidemiological curves to go down from January. Germany, after the cases of administration-related thrombi related to the administration of AstraZeneca, has decided to complete the guideline in citizens below 60 that received the first dose of this brand with the formulation from a different pharmaceutical company.