The World Health Organization (WHO) has warned there is “no evidence” that people with antibodies to Covid-19 have necessarily acquired immunity to the disease and are protected against a second infection.
Some countries, such as Germany, are looking to roll out “immunity passports” that would allow people to be free from some lockdown measures if they can prove they have recovered from Covid-19. However, the WHO has warned governments against this idea as the effectiveness of antibody testing has not been proven.
“As of 24 April 2020, no study has evaluated whether the presence of antibodies to SARS-CoV-2 [the virus that causes Covid-19] confers immunity to subsequent infection by this virus in humans,” the WHO said in a scientific brief published on Friday, April 24.
As such, the introduction of “immunity passports” could actually help to increase virus transmission. "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 organization said
After the body’s immune system initially responds to infection with white blood cells, it starts to produce antibodies that specifically bind to the virus and neutralize the pathogen. The body also makes T-cells that recognize and eliminate other cells infected with the virus, a process known as cellular immunity. After the virus is cleared from the body, some of these specific antibodies will float around for some time, protecting the body from the infection and keeping guard in case of any future invasion. So, if you have specific antibodies to a pathogen in your body, it can suggest you have some level of immunity to that disease.
However, as ever, it's not quite as black and white as that. It might be possible for a person to just have low levels of antibodies in their blood, but not have full cellular immunity to the disease, such as T-cell immunity.
It’s also unclear how long the antibodies for SARS-CoV-2 will hang around. With other coronavirus infections, such as SARS, we know people can produce antibodies against the illnesses for up to three years following infection. Since SARS-CoV-2 is a novel virus, however, we know very little about how it behaves and how long the body’s “immune memory” lasts.
“There remain many unknowns,” pointed out Dr Tom Wingfield, Senior Clinical Lecturer and Honorary Consultant Physician at the Liverpool School of Tropical Medicine.
“These include how long SARS-CoV-2 antibodies will last following infection and whether having these antibodies means that a person is immune to further SARS-CoV-2 infection.”
The WHO, along with much of the scientific community, argues all of this uncertainty means there isn’t enough research yet to guarantee the accuracy of an “immunity passport" – unless an effective vaccine is developed promptly. Although it's clear, the sooner we have a vaccine the better, in the meantime it's best to proceed with caution. Jumping the gun on any action dealing with Covid-19, whether it's a hailed treatment or lifting lockdown measures too soon, could result in making the situation worse not better.
“So-called ‘immunity passports’ for previously infected people are political inventions built around complex scientific concepts. Only a safe and effective vaccine, that I believe will come in the future, will deliver widespread immunity from infection,” said Prof James Naismith, a structural biologist at the University of Oxford.