Pfizer antibody is a RNA based vaccine, which targets the spike protein in Covid-19 virus. There are new variants of the virus identified across the world. These virus variants have mutations in the spike protein. Researchers from the University of Texas genetically engineered several variants of SARS-CoV-2, including one that has the same mutations as the variant called B.1.351, which was first identified in South Africa. The team then tested the antibody efficacy against these variants and found that vaccine was able to neutralize the virus only one-third as effectively as the original Covid-19 strain. 
 
For more information: Y. Liu et al. N. Engl. J. Med. https://doi.org/fwsc; 2021

Scientists at Adimab in New Hampshire isolated several antibodies from the memory B cells (immune cells) of a person, who had survived a SARS infection in 2003. The researchers engineered these antibodies and created a new ADG-2, a new antibody that was particularly effective at disabling SARS-CoV-2 and several related coronaviruses in lab experiments. ADG-2 was also effective in treating SARS-and COVID-19 infections in mice. 

What makes ADG-2 antibody different than others? It recognizes a highly conserved epitope on the surface of these viruses, which authors compare to the Achilles’ heel, making ADG-2 a promising therapy candidate that more effective and broad range than other antibodies. 
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https://science.sciencemag.org/content/early/2021/01/22/science.abf4830