Reuters news agency reported on Wednesday that US pharmaceutical company Johnson & Johnson (J&J) (NYSE:JNJ) has begun a final 60,000-person trial of a single-shot COVID-19 vaccine that potentially would simplify distribution of millions of doses, as compared with leading COVID-19 vaccine rivals using two doses.

In a joint press conference with officials from the National Institutes of Health and the Trump administration, Dr Paul Stoffels, J&J's chief scientific officer, said that the company expects results of the Phase III trial by 2020 end or early in 2021.

According to Dr Stoffels, J&J would publish a detailed study protocol for its phase 3 trial on the company's website, joining the three other vaccine makers that have made these study plans available in recent weeks after calls for increased transparency in the trials. J&J had reportedly started the phase 3 trial after seeing positive results in its phase 1/2 trial in the US and Belgium and plans to release those results imminently.

Dr Stoffels was also quoted as saying that the safety and level of protection in the study were on par with what was seen in the company's animal studies and said the results showed a single dose could offer sufficient protection "for a long time."

J&J's late-stage trial will use as many as 215 sites in the US, South Africa, Argentina, Brazil, Chile, Colombia, Mexico and Peru. The company plans to manufacture as many as one billion doses in 2021 and more after that.

The goal of the trial is to test whether the vaccine can prevent moderate to severe COVID-19 after a single dose, but it will also look to see if the vaccine can prevent serious disease requiring medical intervention and whether it can prevent milder cases of the virus.

Reportedly, Dr Stoffel predicts that it will take six weeks to two months to enrol the trial and he said the company hopes to get an answer on whether the vaccine works "around the end of the year or early next year."

Reuters added it is not clear how fast the company could get regulatory approval, but J&J plans to manufacture doses before approval, so it could start distribution quickly.