An express study to investigate the effects of the combination of Pfizer and AstraZeneca vaccines

Carlos III Health Institute (ISCIII), public research body dependent on the Ministry of Science and Innovation and the Ministry of Health of Spain, will be the promoter of a clinical trial, called CombivacS, which will analyze the possible protective effect and safety of administering a dose of Pfizer to people who have already received a first dose of the vaccine from the AstraZeneca laboratory, after a minimum of 8 weeks has passed since this dose.

As the institute announced in a statement, the clinical trial, which was launched after the suspension of vaccination with AstraZeneca serum in people under the age of 60, seeks to provide scientific evidence to support decision making regarding a possible alternative to full vaccination in these people. In other words, the study aims to clarify whether people who received the first dose of AstraZeneca have generated enough antibodies or whether a booster dose with another vaccine is needed.

During the clinical development of the Pfizer and AstraZeneca vaccines, different studies were developed to define the dose, efficacy, safety and conditions of use of each of them individually.

After approval from health authorities, both have been available for some time and administered in Europe, but, so far, there are no clinical data on their possible combined use. “Joint use seems possible and even desirable”, According to experts from this Spanish institute, “Since these are vaccines that work with different mechanisms of action and this way of treating other diseases has been shown to be beneficial, but clinical trials like this are needed to verify this. “

The CombivacS study is one of the first clinical trials to examine the safety and immunogenicity of this type of combination regimen. It will be held in five hospitals: La Paz and Clínico San Carlos de Madrid; Vall d’Hebron and Clínic, in Barcelona, ​​and Cruces in Vizcaya. ISCIII’s National Microbiology Center (CNM) will act as the central laboratory for the trial, which has received scientific advice from the Spanish Agency for Medicines and Health Products (AEMPS). AEMPS, after approval of the protocol by the Pharmaceutical Research Ethics Committee (CEIm) of La Paz University Hospital in Madrid, issued the necessary authorizations for its implementation.

Test development and characteristics

It is a phase 2, controlled, randomized and adaptive clinical trial to assess safety and immunogenicity (ability of the immune system to respond successfully to infection) from a dose of the vaccine called Comirnaty (Pfizer) in people who have previously received a dose of Vaxcevria (AstraZeneca) vaccine.

In this way, study examines possible combination of more than one vaccine (heterologous vaccination schedule), with different mechanisms of action, to complement the desired immunization. The initial hypothesis is that said immunogenicity will be greater in the group receiving two different doses of vaccines compared to the single dose.

The main objective of the trial is therefore check if in people who have already received a dose of AstraZeneca vaccine, there is a significant increase after 14 days in their antibody levels against SARS-CoV-2 after receiving a dose of Pfizer.

To assess this possible increase in antibodies, the number of antibodies in a group of people who have been previously vaccinated with a single dose of AstraZeneca but who will not initially receive the dose of Pfizer will be analyzed simultaneously.

In CombivacS, 600 people randomly selected from among those who have received a dose of the AstraZeneca vaccine will participate, provided that a minimum of 8 weeks has elapsed between this dose and the time of the start of the trial and they are under 60 years of age

In all cases, the first results are expected 5 weeks after the start of the trial. If these results were favorable in terms of safety and efficacy of the sequential vaccination schedule, a dose of Pfizer will be offered to all participants in the control group.

The comparison of the immune response between the two groups will be carried out on analyzes obtained 14 days after the inclusion of each volunteer, without prejudice to other very exhaustive analyzes which will be carried out over one year.

The National Microbiology Center-ISCIII will act as the central testing laboratory and will be responsible for the analysis and interpretation of antibody levels. Thus, the biological samples of the participants will be sent to this center for the determination of neutralizing antibodies and antibodies against SARS-CoV-2 as an indicator of protection against COVID-19.

Further, This study will help answer other scientifically relevant questions. Thus, among the secondary objectives, the researchers seek to acquire knowledge on the immune response conferred by the sequential association of the two vaccines over one year., as well as protection against variants of SARS-CoV-2 at 14 and 28 days after the end of vaccination, among others.

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