Hamster can produce high antibody to SARS-2 (see below). So, the result is strange. Or the Hamster already infected by a close strain of coronavirus, the existing immunity suppressed the antigen (you inject) produced antibody.

The Syrian hamster could be consistently infected by SARS-CoV-2. Maximal clinical signs of rapid breathing, weight loss, histopathological changes from the initial exudative phase of diffuse alveolar damage with extensive apoptosis to the later proliferative phase of tissue repair, airway and intestinal involvement with viral nucleocapsid protein expression, high lung viral load, and spleen and lymphoid atrophy associated with marked chemokine/cytokine activation were observed within the first week of virus challenge. The mean lung virus titer was between 105 and 107 TCID50/g. Challenged index hamsters consistently infected naive contact hamsters housed within the same cages, resulting in similar pathology but not weight loss. All infected hamsters recovered and developed mean serum neutralizing antibody titers ≥1:427 14 days postchallenge. Immunoprophylaxis with early convalescent serum achieved significant decrease in lung viral load but not in lung pathology. No consistent nonsynonymous adaptive mutation of the spike was found in viruses isolated from the infected hamsters.

Dear Dr.Shao,

Thank you very much for your kind answer!

The hamsters in our experiments were not previously infected with any coronaviruses.

When we immunized animals with full-length S protein or a DNA vaccine encoding S protein, we did not observe a difference in the immune response of mice and hamsters. All animals developed high titer of anti-S antibody with neutralizing activity.

We now tested the immunogenicity of the RBD protein in rabbits and ferrets. These animals, like mice, respond with high titers anti-RBD antibodies after RBD immunization. But hamsters respond with a very weak titer of anti-RBD and anti-S antibody. Why? The mystery of nature.