A recently published but not peer reviewed study conducted in Sweden suggests that some people might have immunity to SARS-CoV-2, despite testing negative for antibodies.
The human immune system contains many actors. Antibodies, which tag and attack pathogens directly, are just one part of it. T-cells, the focus of the recent Swedish research, are able to identify and kill cells infected by a pathogen. Both have memory and can provide immunity to future infections. Antibodies and T-cells, also known as T-Lymphocytes, typically work together.
The researchers found that despite some people testing negative for SARS-CoV-2 antibodies they still had a T-Cell response. It is not clear why. Some of those tested were infected months earlier, so it may be that their antibody response has faded and the only remaining detectable element of their immune response is a T-Cell response.
The impact of the SARS-CoV-2 T-cell response by itself is not yet fully understood. It is possible that it protects an individual from getting sick but does not stop them from carrying the virus and transmitting it.
The results of this research could have implications for vaccine development.
Overall, 19% of those in the group testing positive for a SARS-CoV-2 T-cell response tested negative for antibodies. Among those with symptoms ranging from mild to asymptomatic, the difference was even greater. Among this group, 26% of those with a SARS-CoV-2 T-cell immune response tested negative for antibodies. These findings suggest that antibody tests might miss a significant percentage of those with potentially some degree of post-infection immunity.
For those who believe herd immunity is the only way out, this research might turn out to be positive news. It might mean a larger percentage of the population has immunity than antibody testing suggests.
For those concerned about the still emerging long-term health impacts of the disease it might be bad news because it suggests more might have been infected than antibody studies suggest.
SARS-CoV-2 has been with us for less than a year and we are still learning about it. Some survivors are discovering they have lung scarring and heart damage. Others who started off with mild symptoms are now reporting persistent symptoms resembling those associated with Chronic Fatigue Syndrome.
The Swedish T-Cell research included 203 Covid-19 survivors with different symptom severity, ranging from asymptomatic to severe. The group was not representative of the general population – the research was focused on understanding the human immune response to SARS-CoV-2 rather than estimating the percentage of the population infected. The study has not been peer reviewed.
Research paper (in English)