US researchers have found the virus behind COVID-19 could have infected far more people than official figures show - up to 85 times as many, or possibly more.
The good news is that would mean the virus isn't nearly as deadly as previously thought - though with no one immune and no proven cure, it still has the capability to overwhelm health systems.
So far there have been a reported 165,000 deaths from of COVID-19 and 2.4 million cases. These only include infections that have been confirmed or deemed likely by each country's health officials though, and as Newshub's Europe correspondent Lloyd Burr discovered recently, even in a wealthy country like the UK it can be difficult to get tested when there's high demand.
The virus can also be asymptomatic, meaning the infected person might not even know they have it, or only suffer mild effects, so don't bother getting tested.
To find out the true spread of the virus, researchers in California tested 3300 people who volunteered to be tested for antibodies to the disease - proteins the body produces to fight off the infection.
After making adjustments to the raw figures to better represent the demographics of the local population, it was estimated between 2.5 and 4.2 percent of the Santa Clara region were infected. That's as many as 81,000 people - at the time the testing was carried out, there were fewer than 1000 reported cases in the area.
"The population prevalence of SARS-CoV-2 antibodies in Santa Clara County implies that the infection is much more widespread than indicated by the number of confirmed cases," their paper, uploaded at the weekend and not yet peer-reviewed, reads.
"Several teams worldwide have started testing population samples for SARS CoV-2 antibodies, with preliminary findings consistent with a large under-ascertainment of SARS CoV-2 infections."
The US has had more confirmed infections and deaths from the virus than any other country, with health authorities' advice often being dismissed by state and federal politicians.
The mortality rate for COVID-19 remains a mystery, with an early WHO estimate being as high as 3.4 percent. But that was based on deaths compared to confirmed cases of the disease - while few deaths would go unreported, the California scientists' findings suggest the case numbers could be vastly underestimated. The mortality rate for COVID-19 could be as low as 0.12 percent, they say, which would make it only slightly more lethal than influenza.
But influenza only infects a fraction of the population each year as it's not as infectious as COVID-19, many simply won't catch it and there are vaccines available. No one in the world, prior to catching it, is immune to COVID-19 as it's caused by a brand new virus - which is why it's been able to wreak such havoc in countries like Italy and Spain, which were hit early and were unprepared, or the UK, which initially went for a 'herd immunity' model but eventually changed tack and followed most other countries into lockdown.
Epidemiologist Krys Johnson of Temple University in Philadelphia told Live Science even in the hardest-hit city in the world - New York, where 0.1 percent of the entire population has been killed - there probably wouldn't be herd immunity yet.
She also said it was difficult to estimate the mortality rate based on the Santa Clara study, particularly with other parts of the US having higher rates of obesity and other conditions known to increase the severity and lethality of the disease.
It's still unclear if people who have recovered from the disease are truly immune, with reports of patients falling ill again after recovering.
"A lot of preliminary information coming to us right now would suggest quite a low percentage of [the] population have seroconverted [to produce antibodies]," Mike Ryan, the World Health Organization's top emergencies expert, said on Friday.
"The expectation that ... the majority in society may have developed antibodies, the general evidence is pointing against that."
Studies earlier this year suggested catching the disease once was enough to develop an effective immune response, but the researchers were looking at infected monkeys, not people.
New Zealand's random testing has failed to pick up any evidence of widespread transmission of the virus in the community, and the confirmed cases are largely linked to known clusters of infections, generally brought in from overseas. The number of new reported cases has plummeted in the past couple of weeks, as the lockdown minimises chances for the virus to infect new victims.
So far 0.02 percent of New Zealanders have tested positive for the virus.
A vaccine for COVID-19 isn't expected to be ready until next year.
