A COVID-19 vaccine developed by Pfizer Inc. and BioNTech SE studied on tens of thousands of people has proven more than 90 percent effective, the companies announced on Monday.

“Their vaccine has been tested on 43,500 people in six countries and no safety concerns have been raised,” BBC reports. “There are around a dozen in the final stages of testing – known as a phase 3 trial – but this is the first to show any results. It uses a completely experimental approach – that involves injecting part of the virus’s genetic code – in order to train the immune system. Previous trials have shown the vaccine trains the body to make both antibodies – and another part of the immune system called T-cells to fight the coronavirus. Two doses, three weeks apart, are needed. The trials – in US, Germany, Brazil, Argentina, South Africa and Turkey – show 90% protection is achieved seven days after the second dose.”

Bloomberg reports: “Eight months into the worst pandemic in a century, the preliminary results pave the way for the companies to seek an emergency-use authorization from regulators if further research shows the shot is also safe. … The data do have limits. For now, few details on the vaccine’s efficacy are available. It isn’t known how well the shot works in key subgroups, such as the elderly. Thoseanalyses haven’t been conducted. And it isn’t known whether the vaccine prevents severe disease, as none of the participants who got Covid-19 in this round of analysis had severe cases, Gruber said.”

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