Pfizer looks at coronavirus vaccine with fewest side effects

Pfizer and its German partner BioNTech will take its Covid-19 vaccine candidate with the fewest side effects into final-stage testing.

In an online report Thursday, Pfizer researchers compared data from early-stage testing of two vaccine candidates. Both revved immune systems similarly, and neither caused severe side effects.

But one candidate caused considerably fewer injection reactions, particularly in older adults -- symptoms such as fever, headache, chills or muscle pain that are temporary but unpleasant, Pfizer reported.

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Final testing of Pfizer's lead candidate has begun as researchers recruit about 30,000 people in the US and other countries. It's one of a handful of experimental vaccines to reach end-stage tests around the world.

It generally takes years to develop a safe and effective vaccine for widespread use and distribution. US health officials hope to start offering vaccinations sometime next year.