A second round of random testing in Spain for antibodies to the new coronavirus indicates that a third of those infected do not develop symptoms, Spanish health authorities said Thursday.

"It is a wake-up call for public health: it is not possible to control (an outbreak) by just considering those who are symptomatic," National Epidemiological Center Director Marina Pollán said.

"With this number of asymptomatic cases, we must follow the recommendations" for personal hygiene and social distancing, Pollán said.

Results from the latest round of the nationwide testing confirmed preliminary finding published three weeks ago showing that blood tests detected the IGG antibody against the virus in only 5% of the 63,000 participants.

Researchers say that means Spain is far from having developed a "herd immunity" to COVID-19 and is still vulnerable to more outbreaks.

Over 95% of the people tested in the first round continued in the study for the second round. There will be one more round of testing before the study concludes.

Spain is rolling back the rules of the country's two-month lockdown. The country was one of the hardest-hit by the pandemic in the world with over 27,000 virus-related deaths.

The Health Ministry's top virus expert, Fernando Simón, acknowledged that regional authorities are "correcting" their data and said he expects the national totals of deaths and infections to undergo revisions.

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