The mutant coronavirus strain that first emerged in recent months in the U.K. is 30% more deadly than original virus, British Prime Minister Boris Johnson announced Friday.

British officials say COVID-19 variant discovered in UK may be 30% more lethal. LONDON – British Prime Minister Boris Johnson warned Friday that a coronavirus variant first detected in the country in September may be around 30% more deadly than previous versions of the disease.

The Covid-19 vaccines authorized in the U.S. are approximately 95% effective at preventing people from getting sick with symptoms, according to Pfizer and Moderna, the companies that produce them.

Some immunity starts 10 to 14 days after the first dose, but full immunity appears seven to 14 days after the second, according to the studies. “If you get just one shot,” Cohen said, “we don't know how long the immune response will last or if one dose will even do anybody any good.”