The news: An experimental covid-19 vaccine being developed by Pfizer and BioNTech provoked immune responses in 45 healthy volunteers, according to a preprint paper on medRXiv. The levels of antibodies were up to 2.8 times the level of those found in patients who have recovered. The study randomly assigned 45 people to get either one of three doses of the vaccine or a placebo. But there were side effects like fatigue, headache, and fever—especially at higher doses. The researchers decided to discontinue with the highest dose, 100 micrograms, after the first round of treatments.

Some caveats required: It’s promising news,but this is the first clinical data on this specific vaccine, and it hasn’t been through the process of peer review yet. Higher antibody levels in patients who’d received the vaccine are a useful proxy for immunity to covid-19, but we don’t yet know for sure that they guarantee immunity. In order to find out, Pfizer will start conducting studies in larger groups of patients, starting this summer. It says its goal is to have 100 million doses of a vaccine available by the end of 2020.

A common approach: Pfizer is using the same experimental technique as Moderna, one of the other pharmaceutical companies developing a vaccine. Both vaccines are designed to provoke an immune response against the coronavirus through its messenger RNA, the genetic instructions that tell the virus how to replicate inside the host. The method could provide a rapid way to develop a vaccine, but it’s yet to lead to a licensed one for sale. Currently, 178 vaccines are in various stages of development; 17 are now going through clinical trials.