|Only 2% to 3% of the global population have developed antibodies to Covid-19, showing that they have been infected and survived the coronavirus. / Photo by: peterschreiber.media via Shutterstock|
Only as few as 2% to 3% of the global population have developed antibodies to Covid-19, showing that they have been infected and survived the coronavirus. according to the World Health Organization (WHO).
Issuance of immunity passports
The current findings by the WHO presents a problem for countries that are hoping to issue immunity passports, a strategy or a certificate that indicates a person can already go back to work because he or she has Covid-19 immunity. The government only needs to conduct reliable antibody testing for people to be issued “back to work” passes. It is believed that this strategy will help a country slowly get back to normal after the lockdown.
American infectious diseases expert Dr. Maria Van Kerkhove, who is also WHO’s technical lead, told The Guardian that the number of people who developed antibodies is lower than expected, doubting whether immunity passports would be an effective policy. Countries that have already explored this possibility of offering immunity passports are Italy, Germany, the UK, and the US. The WHO report suggesting that only 2 to 3% of the global population have developed antibodies to Covid-19 is a blow to hopes of herd immunity among these countries.
“Right now, we have no evidence that the use of a serological test can show that an individual has immunity or is protected from reinfection,” she said. Serologist tests look at people’s blood to see if it contains antibodies.
Herd immunity: indirect protection
There are three ways to stop the virus for good. One involves restricting assembly and movement of people and aggressive testing to stop the transmission. The second option is through vaccines to protect everyone, and the third is herd immunity, which is also somewhat connected to the second option.
Noreen Iftikhar, MD explains that herd immunity happens when a large percentage of the population becomes immune to the infectious disease, so much so that the disease slows or stops from spreading. Herd immunity protects others who have not yet developed the immunity. This is referred to as indirect protection. In most cases, a herd immunity threshold should be observed so that the disease will no longer circulate. It often requires 80 to 95% of the population to be immune to the disease for it to stop spreading but the immunity threshold differs among infectious diseases since not all present the same risk of transmission.
As of 2013, the herd immunity threshold for diphtheria was 85%. For measles, it is between 83 and 94%, polio: 80-86%, pertussis: 92-94%, mumps: 75-86%, rubella: 80-85%, and smallpox: 83-85%, as published by database company Statista.
A California pre-print study also recently found that the number of people infected with the virus is 50 to 85 times more than what the official figures provide. In Santa Clara, California, there were 1,094 confirmed Covid-19 cases when the study was conducted but the antibody test shows that there are between 48,000 and 81,000 people infected during that period. The majority of these cases did not even develop symptoms.
Another study in the Netherlands involving 7,000 blood donors also found that only 3% of them have developed antibodies to Covid-19. Dr. Van Kerkhove said they have to look carefully in the manner these studies were done. This would include knowing how the authors found their subjects and how well the blood test was conducted. She added that they are now working with several countries that are carrying out the serology studies. They are aware that some studies are still in their pre-print version
WHO’s director-general Dr. Tedros Adhanom Ghebreyesus said at a media briefing that easing restrictions will not be the end of the Covid-19 health crisis in any country. He did not entirely dismiss the antibody tests but believes that it should be used alongside more widespread tests to determine whether an individual was actively infected.
The WHO is still welcoming the increasing number of antibody tests performed and Dr. Ghebreyesus said it would help scientists better understand the extent of infection in a given population.
|A California pre-print study recently found that the number of people infected with the virus is 50 to 85 times more than what the official figures provide. / Photo by: Kobkit Chamchod via Shutterstock|
Covid-19 recovery and immunity
Even virologists are not sure if all those who recover from Covid-19 are immune to infectious diseases. Professor of immunology Eric Vivier from a public hospital system in France pointed out how some viral diseases, like measles, confer immunity for life once the person has overcome the sickness. Yet, for RNA-based viruses such as SARS-CoV-2, which causes Covid-19 diseases, it usually takes about three weeks to build up a sufficient quantity of antibodies. At least this is the theory known to them. He recognized the fact that Covid-19 has given one surprise after another in medicine to the point that even epidemiologists and virologists are sure of very little about it.
Recovered Covid-19 patients
From a 58.20% global recovery rate on February 2, it went up to 93.10% on February 28. As of April 19, the global recovery rate stood at 79.11%, according to real-time world statistics platform Worldometer.
Can a person catch Covid-19 twice?
There is little evidence whether individuals who recovered from Covid-19 can catch the diseases a second time but experts are not disregarding the possibility. Several cases in South Korea found patients who already recovered from the infectious diseases later tested positive again for the virus.
University of College London’s director of Genetics Institute Francois Balloux told global news agency AFP, "One can certainly get reinfected, but after how much time? We'll only know retroactively." It could also be a case of false negatives. This happens when the virus never completely disappeared in the body of an infected person but just remains asymptomatic and dormant. This means that a person may remain infected for several weeks. In a study titled "Duration of Antibody Responses after Severe Acute Respiratory Syndrome, authors Li-Ping Wu and colleagues wrote that SARS-specific antibodies were maintained for an average of 2 years and SARS patients may be susceptible to reinfection in 3 years or more after initial exposure.
This is why a vaccine is probably the only real solution the world could rely on instead of herd immunity. Perhaps, using the immunity passport would be premature.
Whether an antibody response means immunity is something that experts have to better understand.