In self-isolating he joins the prime minister and the health secretary, who have both been diagnosed with coronavirus, and the chief medical officer, who is also in quarantine with symptoms.
Friday is also believed to be the last time Mr Cummings was seen on camera, when he was spotted running away from 10 Downing Street after the PM's diagnosis.
With three people close to the prime minister now self-isolating after contracting the illness, of feeling its symptoms, it now seems only a matter of time before others are struck down with the illness.
Chancellor Rishi Sunak and Home Secretary Priti Patel are known to have been near to the prime minister, close to the time he began to feel symptoms.
His pregnant fiance Carrie Symonds, and the 93-year-old Queen - both considered vulnerable to the illness - are believed to have been out of physical contact with him for long enough to believe they're safe.
Johnson says the UK will get through the coronavirus crisis “together” after Britons were warned restrictions on their lives may last for at least six months.
Through the medium of social media video - a channel of communication likely to be used more over comings weeks to comply with social distancing - Mr Johnson PM praised 20,000 former NHS staff who have returned to the service to tackle the pandemic.
And he chose to contradict the “there is no such thing as society” endorsement of pure individualism from his Conservative predecessor Margaret Thatcher.
“We are going to do it, we are going to do it together. One thing I think the coronavirus crisis has already proved is that there really is such a thing as society,” Mr Johnson said.
Mr Johnson, who is suffering with a "temperature and persistent cough", says thanks to the "wizardry of modern technology" he can continue to manage the response by communicating via video.