The US postmaster general has tried to take the heat out of the growing anger about possible disruption to mail-in voting in November’s election by announcing that all proposed operational changes to the postal system will be delayed until after the vote. House speaker Nacy Pelosi said the promise by Louis DeJoy, a Trump appointee whose changes threatened to disenfranchise millions of voters as the pandemic impacts the abulity oif people to vote in person, were “insufficient”. Follow all the voerage of this and the Democratic convention at our US live blog: Testing and contact tracing are crucial measures for slowing the spread of Covid-19, but are not enough on their own to contain the disease, according to a new study by researchers at Imperial College, London. The work published on Wednesday in the The Lancet Infectious Diseases says that test-and-trace can reduce the virus’ reproduction rate, or R number, by 26%, AFP reports. But lead author Nicholas Grassly, a professor at Imperial College’s School of Public Health, said the test and trace work had to be carried out very quickly in order to be effective. That meant immediate testing with the onset of symptoms and results within 24 hours the quarantine of contacts, also within 24 hours; and the identification of 80% of cases and contacts. Very few countries – notably South Korea, Taiwan and Germany – have come close to staying within these guidelines, and most are still falling well short. Australia’s prime minister, Scott Morrison, says it will be compulsory for people to have a Covid-19 vaccine once it is available. Australia had earlier revealed it has agreed a deal with AstraZeneca to supply the potential Oxford University vaccine. People will receive the vaccine for free in Australia, Morrison said, calling the Oxford vaccine “one of the most advanced and promising in the world”. Meanwhile, the Australian state of Victoria, the epicentre of the country’s second wave of infections, recorded 216 new cases in the past 24 hours and 12 deaths, officials said on Wednesday morning. You can follow all the updates from there at our Australia live blog here: Wall Street"s S&P500 hits record high The S&P 500 stock index on Wall Street closed at a record high on Tuesday night marking the complete recovery of shares after the shock of the pandemic. The record confirms that Wall Street’s most closely followed index entered a so-called bull market – or upward curve – after hitting its pandemic low on 23 March. It has surged about 55% since then thanks to massive intervention by the US government and the Federal Reserve central bank. It closed 7.79 points, or 0.23% higher at 3,389.78. That makes the bear market – or downward movement – that started in late February the S&P 500’s shortest in its history. The S&P 500 is a broader index of US companies than the Dow Jones industrial average, which represents only 30 companies. The story of how share prices have roared back as workers around the world find themselves out of a job or on reduced pay is one of the central issues of the pandemic. Read more about how it has panned out in the US here: And from a UK perspective here: Good morning/afternoon/evening. I’m Martin Farrer and thanks for joining me for live coverage of the coronavirus pandemic. Here are the main developments in the past 24 hours: Global coronavirus cases are approaching 22 million and the global death toll has risen to almost 776,000. The biggest drivers of the case counts are the United States and Brazil, according to John Hopkins University. The US has recorded over 5.45 million cases and more than 170,000 lives have been lost. Stocks on Wall Street’s S&P500 index hit an all-time high on Tuesday night completing their recovery from the pandemic shock. The world’s most closely watched measure of share prices has increased 55% since its coronavirus low on 23 March after huge government and central bank stimulus. Young are not invincible amid the coronavirus pandemic, the World Health Organization warned. The WHO said Covid-19 is now being spread mainly by people in their 20s, 30s and 40s, who may be unaware they are infected, potentially transmitting the disease to more vulnerable groups. “We are seeing young people who are ending up in ICU. Young people are dying from this virus,” WHO epidemiologist Maria Van Kerkhove said. The Netherlands could go “back to square one” if the country doesn’t control new infections, the Dutch PM, Mark Rutte, warned. Without imposing mandatory restrictions, Rutte gave people urgent advice not to hold parties at home and to limit events like birthday celebrations and other private house gatherings to a maximum of six people. A hotel quarantine security guard in Sydney has contracted Covid-19. The guard most likely was infected by a traveller from the US, officials said, rasing questions about whether nurses should replace security personnel. Ireland’s nationwide coronavirus restrictions are being “significantly tightened” until at least 13 September as cases surged at the fourth highest rate in Europe. Following the rise in the last three weeks, people have been urged to restrict visitors to their homes, avoid public transport and for older people to limit their contacts. “We’re absolutely not at a stage where we can return to normality. We are at another critical moment,” the taoiseach, Michael Martin, said. Germany is expected to extend its pandemic furlough scheme to 24 months. The chancellor Angela Merkel indicated she welcomed the proposal to let the kurzarbeit programme run on until 2021. A final decision is expected on 25 August. Lebanese authorities announced a new lockdown and an overnight curfew to rein in a surge in infections. The new measures will come into effect on Friday and last just over two weeks. Areas damaged by the devastating explosion that hit Beirut on 4 August will be exempt from the restrictions, as clean-up efforts continue across multiple neighbourhoods. South Africa will launch clinical trials of a US-developed coronavirus vaccine with 2,900 volunteers this week. It’s the second such study in the African country worst hit by the disease. Known as NVX-CoV2373, the vaccine was developed by US biotech company Novavax from the genetic sequence of SARSCoV2. It will be administered to the first volunteer in the randomised, observer-blinded trial on Wednesday.