According to a study published in the Journal of Nature Medicine, recovered COVID-19 patients may rapidly lose antibodies – the blood proteins necessary to stave off virus infections and the cornerstone of vaccinology.
The finding raises new questions about the idea of immunity passports (a way for people considered immune to the virus to move around freely and not need to wear facemasks) and could be cause for concern about the development of an effective vaccine.
Researchers in the study tested for antibodies in 37 people who had fallen ill and recovered from the virus in the Wanzhou district of China. They also tested 37 others who had tested positive for the virus but never showed symptoms – what is known as asymptomatic cases.
This was in order to address two key questions that will inform how the world responds to the pandemic in the coming months – Do most people develop immunity after infection? And how long does that protection last?
In terms of the participants of the study – antibodies for the coronavirus only seemed to last a few months. About eight weeks after recovery, antibodies dropped to undetectable levels in 40% of the asymptomatic people and in 13% of those who had symptoms.
Asymptomatic participants overall had weaker immune responses, those that showed symptoms were less likely to lose their antibodies. It’s unclear if low levels of antibodies, even undetectable levels, are enough to confer immunity. Further research suggests that even low antibody counts could still be enough to prevent reinfection.
Business Insider writes that this study is amongst some of the first into the immune response among asymptomatic people; previous studies have found that most people who show COVID-19 symptoms develop antibodies.
It is also important to note that the Wanzhou study used a very small sample size. Usually, such studies would utilise very large sample groups to be able to generate an empirical generalisation.
Two types of Antibodies
The Wanzhou researchers tested for two types of antibodies – immunoglobulin G (IgG) and immunoglobulin M (IgM).
Human bodies make IgM first in response to a viral infection, then IgG develops over a longer period of time. That means IgG is a better indicator for long-term immunity.
“Even though we don’t know what’s going on with this disease yet, if IgG confers immunity, that’s the more important one that has implications for going back to work,” Ania Wajnberg, the director of clinical antibody testing at Mount Sinai Hospital in New York told Business Insider.
In terms of the study, seven participants from the asymptomatic group and six from the symptomatic group did not test positive for IgG (long-term) antibodies three to four weeks after they were exposed to the virus. Even more participants did not have detectable levels of IgM (short-term antibodies).
After eight weeks total, IgG levels had declined in all but three of the people who started out with detectable levels. The drop was steep: a median decrease of 71% for the asymptomatic group and 76% for the symptomatic group. Some participants no longer had detectable IgG at all.
Importantly, antibodies are not the only way the body fights off infection. White blood cells – T cells and B cells kill viruses and produce new antibodies, respectively – were not measured in the new study.