Immunity Passports Are ‘Not Ready For Prime-Time’

The World Health Organization (WHO) published a scientific brief for governments that have suggested that the detection of antibodies to the SARS-CoV-2 coronavirus could serve as the basis for an “immunity passport” or “risk-free certificate”.

These proposed documents would enable individuals to travel or to return to work, assuming that they are protected against coronavirus re-infection, which could lead to COVID-19 disease.

However, the WHO said on April 24, 2020, 'There is currently no evidence that people who have recovered from COVID-19 and have antibodies are protected from a 2nd infection.'

Furthermore, the WHO says ‘people who assume that they are immune to a second infection because they have received a positive test result may ignore public health advice.’ 

‘And, the use of such certificates may, therefore, increase the risks of continued transmission.’

The WHO said in this statement that it ‘continues to review the evidence on antibody responses to SARS-CoV-2 infection.’

Most of these studies show that people who have recovered from infection have antibodies to the virus. 

However, some of these people have very low levels of neutralizing antibodies in their blood, suggesting that cellular immunity may also be critical for recovery.

Laboratory tests that detect antibodies to SARS-CoV-2 in people, including rapid immunodiagnostic tests, need further validation to determine their accuracy and reliability.

Inaccurate immunodiagnostic tests may falsely categorize people in two ways. 

The first is that they may falsely label people who have been infected as negative, and the second is that people who have not been infected are falsely labeled as positive. 

Both errors have serious consequences and will affect control efforts. 

These tests also need to accurately distinguish between past infections from SARS-CoV-2 and those caused by the known set of 6 human coronaviruses. 

Four of these viruses cause the common cold and circulate widely. 

The remaining two are the viruses that cause Middle East Respiratory Syndrome and Severe Acute Respiratory Syndrome. 

People infected by any one of these viruses may produce antibodies that cross-react with antibodies produced in response to infection with SARS-CoV-2.

Many countries are now testing for SARS-CoV-2 antibodies at the population level or in specific groups, such as health workers, close contacts of known cases, or within households. 

The WHO supports these studies, as they are critical for understanding the extent of – and risk factors associated with – infection.

These studies will provide data on the percentage of people with detectable COVID-19 antibodies, but most are not designed to determine whether those people are immune to secondary infections.

The development of immunity to a pathogen through natural infection is a multi-step process that typically takes place over 1-2 weeks. 

The body responds to a viral infection immediately with a non-specific innate response in which macrophages, neutrophils, and dendritic cells slow the progress of the virus and may even prevent it from causing symptoms. 

This non-specific response is followed by an adaptive response where the body makes antibodies that specifically bind to the virus. These antibodies are proteins called immunoglobulins. 

The body also makes T-cells that recognize and eliminate other cells infected with the virus. 

This is called cellular immunity. 

This combined adaptive response may clear the virus from the body, and if the response is strong enough, it may prevent progression to severe illness or re-infection by the same virus. This process is often measured by the presence of antibodies in the blood.

As new evidence becomes available, the WHO said it will update this scientific brief.

SARS-CoV-2 outbreak news published by CoronavirusToday.