Randomized, open, multicenter, collaborative and adaptive non-inferiority trial to evaluate the immunogenicity and reactogenicity of the heterologous vaccination schedules made up of the combination of vaccines available in Argentina (Sputnik-V, AstraZeneca, Sinopharm and Moderna); and to compare the immunogenicity and reactogenicity of heterologous and homologous vaccination schedules.

More than a hundred COVID-19 vaccines based on different technologies are currentlyin the clinical phase of development around the world. More than a dozen derived from different platforms have been approved by regulatory entities in several countries and are used to immunize the world's population.

The dynamics of the COVID-19 pandemic, the emergence of variants, the magnitude and durability of the immune response, the effectiveness of approved vaccination schemes, as well as the possibility of combining vaccines from various platforms, are some of the issues to be facedin public health decision-making, in order to deliver the best protection standards to the population.

Given the dynamics of the disease in Argentina, the access to different COVID-19 vaccination alternatives requires the development of various strategies, such as stratifying the population sampled by the risk of being infected or transmitting the disease, the agreement for the acquisition of vaccines produced by multiple laboratories simultaneously, setting as a priority first dose vaccination to a higher number of people in a shorter period of time and completing the schemes already started.

The pandemic has revealed the capacity of our country to carry out research studies that produce evidence to face the new challenges posed by COVID19 and, particularly,to implement vaccination as one of the main tools to reduce the health impact it generates-for example,six months after the start of the vaccination campaign, results demonstrate the positive impact of this strategy and its effectiveness.

Models based on heterologous immunization schemes with vaccines from different platforms require evaluation by means of clinical trials,in order to show whether they are not less effective than homologous schemes already established. This is achieved through comparative evaluation of their immunogenicity, efficacy and reactogenicity with studies considering implementation possibilities, adaptiveness and response to real life situations.

Hence, the Ministry of Health propoundsthe development of a collaborative network for the integration of studies on vaccination strategies against COVID-19 with the use of heterologous schemes based on the evaluation of their non-inferiority, compared to homologous vaccination schedulesalready implemented worldwide.

The Argentine Ministry of Health looks forward to generating solid scientific evidence that supports decision-making in health policies, with broad federal participation and common objectives.

Inclusion Criteria:

• 18 years of age or older, vaccinated with 1 dose of Sputnik V, AstraZeneca or Sinopharm vaccine up to 60 days prior to enrollment (according to the platform of the vaccine received as the first dose) or not vaccinated for the mRNA-1273 / mRNA-1273 Arm
• With and without identified risk factors for COVID-19
• Signature of the informed consent
• Remain in the jurisdiction where your study began until the end of it
• Be able to understand and sign the informed consent

Exclusion Criteria:

• Patients with immunocompromise due to underlying disease or immunosuppressive treatment
• Pregnant and breastfeeding people
• Being registered in the National Health Surveillance System for having suffered COVID-19 (symptomatic or asymptomatic) or having a positive IgG result in nucleocapsid ELISA in the sample taken on "DAY 0" for people who had received Sputnik-V or AstraZeneca as the first dose
• Having had a severe allergic reaction (anaphylaxis) to any vaccine