Prime Minister Jacinda Ardern has announced further measures to protect New Zealand against Covid-19 as the world enters a "dangerous new phase".
The hottest week of the year in Britain could lower coronavirus transmission rates, with a study showing that strong summer sunlight causes the virus to decay to almost nothing in just 30 minutes.
Temperatures are forecast to rise above 30C on Thursday, which could draw crowds to beaches and parks as the UK enjoys warmer conditions than Ibiza.
But although mass gatherings might suggest a rise in transmission, new research by retired virologists from the US Army and the US Food and Drug Administration (FDA) shows that sunlight kills off coronavirus extremely quickly, meaning people are likely to be far safer outdoors.
In fact, being indoors in lockdown may have been harmful for people, the study suggests.
People raise hands to the first rays of sunlight at the Mirador Jach'a Apacheta de Munaypata, in Bolivia. Indigenous communities are celebrating the Andean new year 5528. AP Photo / Juan Karita
During peak sunshine in London – which occurs during the summer solstice around June 21 – just 30 minutes of sunlight is enough to reduce the infectivity of coronavirus by 90 per cent.
It means that even if someone was infected and coughed or sneezed onto an outdoor surface, the virus would be largely harmless within half an hour with just a tiny viral load remaining.
The effect of sunlight on the virus is far greater at this time of year. During the autumn equinox, on September 22, it would take one hour and 17 minutes to render the virus largely harmless in the capital, and nearly three hours at the spring equinox (March 20).
Researcher Dr Richard Hobday says sunlight was used on critically ill influenza patients during the 1918 pandemic and reduced deaths. Photo / YouTube
At the winter solstice, on December 21, the virus could survive for more than five hours in the weak sunlight, although indoors it is likely to last for days.
For British cities at a more northerly latitude – such as Newcastle, at 12.7C – it would take slightly longer for the same disinfecting effect; around 34 minutes in midsummer, one hour 40 minutes in the autumn, nearly four hours in the spring and more than five in the winter.
In fact, sunlight is so effective at fighting coronavirus that authors Dr Jose-Luis Sagripanti and Dr David Lytle argue that lockdown measures could actually have harmed people and increased viral spread.
"Forcing people to remain indoors may have increased or assured contagion of Covid-19 among same household dwellers and among patients and personnel inside the same hospital or geriatric facilities," they wrote in the journal Photochemistry and Photobiology.
"In contrast, healthy people outdoors receiving sunlight could have been exposed to a lower viral dose with more chances for mounting an efficient immune response.
"The viral persistence estimated here for cities at northern latitudes where Covid-19 expanded rapidly during winter 2019-2020 and relatively higher viral inactivation in more southern latitudes receiving high solar radiation during the same period, suggests an environmental role for sunlight in the Covid-19 pandemic."
Weather maps show a 1126km-wide plume of tropical air moving towards Britain, with temperatures likely to rise above 30C, making Thursday the hottest day of the year so far – beating May 20, when the mercury hit 28.2C in Suffolk.
Met Office forecaster Marco Petagna said: "34C looks a distinct possibility on Thursday." Weather Outlook forecaster Brian Gaze added: "June has been flaming wet, but will switch to flaming hot."
Sunlight includes ultraviolet radiation which damages the DNA of viruses. Viruses tend to survive better in cold weather because they have a fatty protective coating which degrades when it is warm. While the melting of the coating allows the virus to invade the warmth of the body, it dies if the casing disintegrates outside.
A new study from the US National Biodefense Analysis and Countermeasures Center also found that coronavirus floating in the air decays by 90 per cent in just six minutes of summer sunshine and 19 minutes of winter sunlight.
During the Spanish Flu pandemic of 1918, doctors noticed that patients who were nursed outdoors appeared to fare better.
High temperatures may also play a role. One study by Harvard University showed that at 6C in dry weather, flu survived on a surface for more than 23 hours, but at a temperature of 32C it was dying within an hour.
Bright sunlight can quickly heat up surfaces beyond 32C even if the outside air temperature is lower.
Britain experienced the sunniest April on record, which has coincided with a substantial fall in new cases. The UK had an average of 224.5 hours of sunshine, compared with 211.9 hours in April 2015, the previous highest.
Researcher Dr Richard Hobday, author of The Healing Sun and The Light Revolution, said: "Sunlight was used on critically ill influenza patients during the 1918 pandemic. This reduced deaths from 40 per cent to 13 per cent.
"The finding that sunlight kills the virus in aerosols could be significant."
The University of Oxford also recently conducted a review into whether climate conditions were playing a role in the transmission of coronavirus, also found that cold and dry conditions appear to boost spread.
