The virus is proving to be remarkably stealthy.

Iceland is a small nation of about 364,000 people with strong healthcare and a supportive social system. While most affected countries are only testing those who display severe symptoms, Iceland wants to test everyone in the country for the novel coronavirus.

It can afford to do so in part thanks to its relatively low population, but also due to its well-organized and well-funded medical system. Iceland has currently carried out 10,000 tests — this is far less than what other countries have done, but on a per capita basis, Iceland ranks first in the world.

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“Iceland’s population puts it in the unique position of having very high testing capabilities with help from the Icelandic medical research company deCode Genetics, who are offering to perform large scale testing,” Thorolfur Guðnason, Iceland’s chief epidemiologist, told BuzzFeed News. “This effort is intended to gather insight into the actual prevalence of the virus in the community, as most countries are most exclusively testing symptomatic individuals at this time.”

Not all the results from Iceland’s tests have come through yet, but the ones that have, show that half of all cases are asymptomatic (at the time of testing).

This would suggest that, on one hand, the virus is not as dangerous as we thought, but on the other hand, it would also suggest that it has spread far more than we are currently aware of.

These results are also indicated by a testing survey carried on an entire Italian town of Vo (population 3,300), where the results showed that more than 50% of all cases are asymptomatic.

The whole population of the village was tested, and 3% of the residents tested positive. Then, after a two-week lockdown, the population was tested again. The transmission had been reduced by 90% and the results were confirmed: the majority of cases seem to be asymptomatic.

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Luca Zaia, the governor of the Veneto region told Italian media this week:

“We tested everyone, even if the ‘experts’ told us this was a mistake: 3,000 tests. We found 66 positives, whom we isolated for 14 days, and after that 6 of them were still positive. And that is how we ended it.”

This strongly emphasizes the need for mass testing, as quickly as possible.

This is still a rapidly unfolding situation where we are learning new things every day. It’s important to have a bigger-picture understanding of how the infection spreads. Of course, there is a finite government testing capacity, but expanding that capacity can pay great dividends in both the short and the long run.

Similar studies carried on Chinese patients report similar things: the virus is spreading far more than we are anticipating. For every known case, there are five or ten people whose symptoms go undetected.

“Covid-19 is proving to be a “stealth virus” in that we now know a significant amount of transmission is through people who don’t have symptoms. The exact % will depend on setting, but is high enough to make testing and surveillance key tools,” said Dr. Jonathan Quick in a Reddit AMA.

The World Health Organization also urges countries to expand their testing capacity as much as possible.

“You cannot fight the fire blindfolded, and we cannot stop this pandemic if we don’t know who is infected,” director-general Dr Tedros Adhanom Ghebreyesus said this week. “We have a simple message for all countries: Test, test, test. Test every suspected case.”

For each and every one of us, there is also an important lesson to apply: we should all act as if we have COVID-19. You may only have a sour throat or a mild cough, you might not have any symptoms at all — you could still be carrying the disease.

As authorities expand testing capacity, and as researchers work on treatments, it’s important that we play our part and prevent the spread of the disease.