People who have had COVID-19 are highly likely to have immunity to it for at least five months but there is evidence that those with antibodies may still be able to carry and spread the virus.
But experts cautioned that the findings mean people who contracted the disease in the first wave of the pandemic in the early months of 2020 may now be vulnerable to catching it again.
"I'm becoming more and more obsessed with what we can do," Johnson said, adding that the green agenda provided an opportunity to aid economic recovery from the COVID-19 pandemic.
Brent crude prices were down 46 cents at $56.12 a barrel by 12:43 p.m. EST (1743). An earlier rise took prices as high as $57.42 a barrel, the strongest since Feb. 24.
Health emergency coordinator Fernando Simon blamed the surge on lax restrictions over the Christmas holidays and said he expected the increase to continue for some time.
The first daily vaccination statistics showed that nearly 2.3 million people had so far received their first doses of a COVID vaccine and nearly 400,000 had received a second dose.
Diana Bell, a wildlife disease expert at the University of East Anglia who has studied the SARS virus, Ebola and other pathogens, said focusing on a particular origin species is misguided.