mRNA vaccines for COVID-19 from BioNTech/ Pfizer and Moderna/NIAID) are safe and effective. Genetic instructions in the form of messenger RNA (mRNA) are packaged in submicroscopic fat "bubbles" called lipid nanoparticles that are taken up by host cells. The mRNA code directs synthesis of the virus's spike protein. Cells display the viral protein on their surface, which immune cells detect and respond to. The "bubbles" are delicate, hence the need for these vaccines to be stored at extremely low temperatures before use. Aside from the cold storage requirements, mRNA vaccines offer advantages over older types of vaccines in efficacy, speed of development, and production scalability and reliability. Though virus-free, the vaccines partially mimic natural virus infection, eliciting a robust immune response. Common reactions include transient symptoms such as fatigue, aches, and fevers. Risk is otherwise minimal since the mRNA acts outside the host cell nucleus and its DNA, and the cell destroys the mRNA after use.