The World Health Organization (WHO) says there is currently “no evidence” showing that people who have recovered from the coronavirus are not at risk of becoming infected again.
“Some governments have suggested that the detection of antibodies to the SARS-CoV-2, the virus that causes COVID-19, could serve as the basis for an ‘immunity passport’ or ‘risk-free certificate’ that would enable individuals to travel or to return to work assuming that they are protected against re-infection.” Further, “there is currently no evidence that people who have recovered from COVID-19 and have antibodies are protected from a second infection,” the WHO said in a scientific brief.
While intended to provide caution for interpreting immunity tests, blanket statements and definite certainties such as these simply incite fear and panic. Yet, is it even true? Is there really NO evidence of immunity?
Animal models suggest protection from re-infection. A study in China published in March revealed that rhesus macaques (monkeys) could not be re-infected after initial COVID-19 episode in the short term (<28 days).
Recovered patients have neutralizing antibodies. Antibodies that may block the virus from infection are called neutralizing antibodies. These antibodies have an important role in viral clearance and protection. The levels of neutralizing antibodies in the blood have been a gold standard to evaluate the efficacy of vaccines against smallpox, polio, and influenza viruses. A recent study demonstrated that COVID-19 patients developed neutralizing antibodies, peaking at days 10-15 after the onset of illness, and remained stable afterwards. In SARS (a different coronavirus), 90% of recovered patients at two years had immune responsive antibodies.
Donor convalescent plasma treatments may be working. Plasma treatments may provide passive antibody (possibly due to the donor neutralizing antibodies mentioned above) and have been beneficial in treating previous viral infections such as Ebola and SARs. In a study of five critically ill patients with COVID-19 treated with plasma, all had a decrease in inflammatory markers and amount of virus detected. In another study with seven patients, convalescent plasma with high donor neutralizing antibodies resulted in an undetectable viral load after treatment.
In short, the WHO’s statement that there is no evidence for immunity to re-infection is misleading and may induce fear and panic. While the current research has significant limitations, there is at least some evidence that suggests short-term immunity. How long that immunity lasts, and the impact on the pandemic is to be determined.
Jesse O’Shea is an infectious disease fellow.
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