Eight out of ten people infected with coronavirus may never show symptoms, meaning the actual infection total could be five times higher, according to an Australian study from an Antarctica cruise.
A cruise ship with mostly Australian and Kiwi passengers left Argentina in mid-March, but quickly turned into a catastrophe when COVID-19 spread aboard.
Eight passengers had to be evacuated to receive care, and one died while the others were flown home.
Of the 217 passengers and crew on board, 128 tested positive for the virus, according to a study led by Professor Alvin Ing of Macquarie University and published today in the journal Thorax.
Of those 128, a total of 104 patients, or 81 percent, had no symptoms. This means that for every sick passenger there were four asymptomatic carriers.
A cruise ship with mostly Australian and Kiwi passengers left Argentina in mid-March, but quickly turned into a catastrophe when COVID-19 spread aboard. Pictured: coronavirus patients in Italy
Melbourne epidemiologist Ivo Mueller told the Australian Science Media Center“If the same pattern is repeated elsewhere, it means that in countries testing only symptomatic cases, the actual burden of infection may be five times higher than currently reported.”
In theory, this means that Australia’s actual total could be over 35,000 instead of the 7,150 officially registered.
Disease expert Professor Sanjaya Senanayake from Australian National University said scientists are struggling to figure out the true percentage of asymptomatic patients.
He said, “There are varying proportions of asymptomatic cases in different studies, including about 40 percent in study from Iceland, 18 percent on another cruise ship, 30.8 percent in Japanese evacuees from Wuhan, and nearly 80 percent in another Chinese study. So it is difficult to know what is right. ‘
The ship set sail from Argentina in mid-March for a planned 21-day cruise in Antarctica, along a similar route explorer Sir Ernest Shackleton had taken in the early 1900s.
It went off after the global pandemic was declared by the World Health Organization and two of the study’s authors were passengers, while a third was the expedition physician.
In early March, the WHO suggested that the number of asymptomatic patients could be as low as one percent, very different from the 81 percent figure on the cruise ship
Passengers and crew were screened for symptoms of Covid-19, body temperatures were measured before boarding, and no one who had recently traveled through countries with high infection rates, such as China and South Korea, was admitted.
The first recorded fever on board the ship was on day eight, and the study authors said that from then on, all passengers were confined to their cabins and surgical masks were issued, while full personal protective equipment was used for any contact with patients with fever .
Eight people had to be evacuated from the ship medically, and the authors said one had died so far.
The Uruguayan government and the Ministry of Health created a ‘sanitary corridor’ for the repatriation of 112 Australian and New Zealand passengers on Day 28 and for all other passengers on Day 32.
Researchers from the Faculty of Medicine and Health Sciences at Macquarie University, the Oncology Trials Department at Sunshine Coast University Hospital, and the Royal Australian College of General Practitioners believe that their study is the first case of complete Covid-19 tests of all passengers and crew on an isolated cruise ship during the current pandemic.
More than 80 percent of the passengers and crew who tested positive for Covid-19 were asymptomatic
Professor Alan Smyth, editor-in-chief of the magazine, said the results of the study could have implications for easing locking restrictions if more people than previously thought had the virus.
He said, “It is difficult to find a reliable estimate of the number of Covid-positive patients without symptoms.
In early March, the WHO suggested the figure might be as low as one percent, very different from the 81 percent figure on the cruise ship.
As the countries come out of the lockout, a large proportion of infected but asymptomatic individuals may mean that a much higher percentage of the population is infected with Covid than expected.
These individuals may be immune to Covid. This demonstrates the urgent need for accurate seroprevalence studies to estimate the overall infection rate of the population worldwide. ‘
It remains unclear what level of immunity people develop once they have had Covid-19.
Coronavirus binds to the ACE2 receptor molecule in lung cells using a spike protein – the tighter it can attach, the less likely it is to be washed away and the sicker it makes its host