evidence: A fourth COVID-19 vaccine has been authorized in the United States. Called Novavax, it's a more traditional vaccine that uses moth cells and tree bark. Instead of an mRNA vaccine (Pfizer, Moderna) or a viral vector vaccine (Johnson & Johnson), Novavax is a subunit protein vaccine. [...] For example, some are allergic to polyethylene glycol (PEG), an ingredient in the mRNA (Pfizer and Moderna) vaccines. There's no polyethylene glycol (PEG) in Novavax. [...] The Novavax COVID-19 vaccine contains a protein (made using moth cells) plus an adjuvant (made from tree bark). An adjuvant is an ingredient added to boost a person's immune response, creating higher levels of antibodies.