More evidence that COVID-19 vaccine mix can help trigger a robust immune response


Eight volunteers who received a full dose or a single dose of an mRNA vaccine or ChAdOx1 vaccine after a dose of a gorilla adenovirus test vaccine showed a significantly elevated level of antibody and response T cells against SARS-CoV-2.

Although several vaccines have now been approved to fight the coronavirus disease (COVID-19) pandemic, several countries are facing vaccine supply shortages. Most two-dose vaccines require both doses to be of the same vaccine. However, with these vaccine supply constraints, researchers began to assess the potential of mixing different types of vaccines.

Such a mix of vaccine types may not only help overcome vaccine availability constraints, but may also be necessary for long-term protection against Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). In addition, using a second dose of a different vaccine may help overcome vaccine hesitation in people who have received a dose of the adenovirus vaccine, which had raised concerns. safety concerns among a number of extremely rare blood clots.

Some countries in Europe, such as Spain and Germany, recommend a booster dose of an mRNA vaccine for people under the age of 60 who have received their first dose of Vaxzevria, manufactured by AstraZeneca.

Mix vaccine technologies

Heterologous vaccination, or vaccination doses using different vaccine technologies, is known to improve the immune response and has been proposed for other viruses and cancers. Vaccination data in mice has provided evidence of the benefit of mixing vaccine technologies, and several clinical trials are underway to test the safety and efficacy of this strategy in COVID-19 vaccines.

Phase I clinical trials of a single dose regimen of a gorilla adenovirus vaccine, GRAd-COV2, have shown that it is both safe and induces good levels of binding antibodies and neutralization.

At the end of the 24-week follow-up, eight volunteers reported that they had received either the full cycle or a single dose of BNT162b2 mRNA vaccine or ChAdOx1 vaccine as part of the Italian national immunization campaign. This occurred between 14 and 24 weeks of the GRAd-COV2 vaccination dose.

Italian researchers measured the immune response to this heterologous vaccination in these eight participants. They found that SARS-CoV-2 spike protein binding antibodies increased significantly from the highest levels recorded at week 12. There was no difference in antibody levels from those who have received two doses or a single dose of different vaccines.

The researchers also measured the response of T cells in the participants. The strong T cell response induced by GRAd-COV2 was further increased after vaccination with mRNA or ChAdOx1 vaccine in five participants. The response of the T cells remained the same in the others.

Potential benefits

Although the number of participants in this study is very small and there are no safety data, the results suggest that the immune response after a single dose of GRAd-COV2 can be significantly enhanced by one dose. unique to another vaccine technology.

Overall, this evidence supports the concept that a single dose of an adenoviral vaccine, which is inexpensive and easy to deploy in a pandemic setting, represents a good tool for effectively priming the immune system, which can be stimulated. subsequently with a single dose of a different vaccine platform, achieving high levels of immune responses, ”the authors write.

The use of adenovirus-based vaccines in the heterologous vaccination strategy may be important in inducing and sustaining the T-cell response, which may provide cross-protection against emerging variants of SARS-CoV-2. Further studies on the safety and optimization of the timing of heterologous vaccination doses will help advance this strategy.

*Important Notice

medRxiv publishes preliminary scientific reports that are not peer reviewed and, therefore, should not be considered conclusive, guide clinical practice / health-related behavior, or treated as established information.


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