Coronavirus: No evidence of immunity after infection, warns WHO

The public health agency raised doubts over the reliability of 'immunity passports'

A lone bugler playing The Last Post on the steps of the Sydney Opera House. Australians and New Zealanders held dawn Anzac Day vigils from the isolation of their own driveways on April 25 to honour their armed forces, as parades were cancelled and ceremonies closed to the public due to coronavirus shutdowns. AFP / Sydney Opera House

Italian President Sergio Mattarella arriving to place a wreath on the tomb of the unknown soldier at the Altare della Patria - Vittorio Emanuele II monument in Rome, as part of a commemoration ceremony for the 75th anniversary of Liberation Day, which marks the fall of Nazi occupation in 1945. AFP

A Palestinian child rides a bicycle along a street decorated with lit up umbrellas in Rafah in the southern Gaza Strip on the second night of Ramadan early on April 25, 2020. AFP

Pet carer Mary Carmen Arreguin, 41, gestures to dogs behind a fence at San Gregorio animal shelter which is promoting pet adoptions as a way of making quarantine more bearable, while the spread of coronaviruscontinues, in El Ajusco, on the southern outskirts of Mexico City, Mexico April 24, 2020. Reuters

Palestinian Walid al-Hattab prepares soup for the poor during Ramadan in Gaza City on April 24, 2020. AFP

Lest We Forget is written in the sky with smoke as two people box at the Breakfast Point Village Green at dawn on Anzac Day in Sydney, Australia, 25 April 2020. EPA

Inmates of the Villa Devoto prison riot in Buenos Aires, Argentina 24 April 2020. A group of prisoners rioted to demand that they be allowed access to the house arrest regime during the Covid-19 pandemic. EPA

William McMaugh poses after a Anzac Day Dawn Service outside North Bondi RSL Club at Bondi Beach on April 25, 2020 in Sydney, Australia. Getty Images

In this image taken with a fisheye lens, cars line up for food at the Utah Food Bank's mobile food pantry at the Maverik Center, Friday, April 24, 2020, in West Valley City, Utah.AP Photo

A man fires a vintage canon to signal the breaking of fast shortly after sunset in Sarajevo, Bosnia, Friday, April 24, 2020. AP Photo

There is no evidence people who have recovered after testing positive for the coronanvirus and have antibodies in their system won't be infected again, the World Health Organisation has warned.

In a briefing note, the WHO questioned if so-called "immunity passports" or a "risk-free certificate" would be reliable given current testing capabilities.

It's hoped these certificates could expedite people's return to the workplace.

Typically the body takes one to two weeks to develop immunity to a pathogen via an infection, the WHO said.

Studies of people who have recovered from the coronavirus typically show they have antibodies to the virus. However, some of these people have very low levels of neutralising antibodies in their blood, the WHO warned.

No study has so far confirmed that the presence of these antibodies offers immunity to a subsequent infection.

The WHO also said more work needs to be done to determine the accuracy and reliability of tests to detect antibodies to the coronavirus.

"At this point in the pandemic, there is not enough evidence about the effectiveness of antibody-mediated immunity to guarantee the accuracy of an “immunity passport” or “risk-free certificate,"" the WHO said.

"People who assume that they are immune to a second infection because they have received a positive test result may ignore public health advice. The use of such certificates may therefore increase the risks of continued transmission."