Would knowing that you were anti-SARS-CoV-2 antibody-positive change your behaviour?
The WHO and other public health agencies are trying to play down the importance of having antibodies to SARS-CoV-2 saying they don’t yet have the data to say these antibodies protect you from reinfection. Yes and no. No in that we don’t have data yet in relation to SARS-CoV-2, but YES in relation to other viral infections.
If you have been infected with SARS-CoV-2, either asymptomatically or symptomatically (COVID-19), and have developed an antibody response (IgM and/or IgG) to the viral proteins then you are likely to be protected from reinfection in the short (months) and intermediated (years) term. We know from other coronavirus infections that these antibody levels wane with time and the protection is lost, which is why we can get repeated infections with other common coronaviruses. I suspect the same may happen with SARS-CoV-2 as well; in other words, immunity may not be life long.
It is also clear that people who have asymptomatic and mild infections have lower antibody levels than people with severe infections and hence their immunity may be less effective and less longlasting. It also seems that having antibodies to other coronaviruses, i.e. previous coronavirus infections, may protect from getting severe COVID-19. The latter implies that some of these antibodies may be cross-protective.
A lot of effort is going into the testing of convalescent plasma from COVID-19 patients, which contains anti-SARS-CoV-2 antibodies, as a treatment in severe COVID-19. The preliminary results are looking promising. In addition, many academic laboratories and pharma companies are trying to develop commercial neutralizing monoclonal anti-SARS-CoV-2 antibodies as a treatment to prevent and treat COVID-19.
All of this evidence, and basic immunology, suggests that having anti-SARS-CoV-2 antibodies is likely to indicate that you will be immune to reinfection in the short to intermediate-term and even if you were reinfected you would get an asymptomatic or mild infection. The whole premise of herd immunity is built on these assumptions, which is why the WHO and public health officials should get off the fence.
But why are they sitting on the fence? I suspect it has to do with behavioural psychology. They don’t want to see antibody-positive people relaxing their guard and acting normally, i.e. no social distancing, no handwashing, no masks, etc. They would set a bad example for people who are antibody negative.
But knowing what I know about virology and immunology if I was antibody-positive it would be a great relief to me and my family. I would be at low risk of getting COVID-19, I could see patients face-2-face without putting them at risk and I could reassure my family that I am not going to infect them. I could even potentially visit and help vulnerable people living near me without fear of infecting them. It is for these reasons that I had my blood taken yesterday to find out if I have had SARS-CoV-2 infection or COVID-19. If antibody-positive then that severe flu-like illness I had over Christmas could have been the sentinel event. There is increasing evidence that SARS-CoV-2 was already circulating in London in December and I was unwell for 3 weeks with many symptoms compatible with COVID-19. If it was that event I could have been infected by patients or staff whilst working on the general medical wards. If on the other hand, if I was antibody negative then I will remain super vigilant and may not cancel my life insurance policy just yet.
Long et al. Antibody responses to SARS-CoV-2 in patients with COVID-19. Nature Medicine (2020), Published: 29 April 2020.
We report acute antibody responses to SARS-CoV-2 in 285 patients with COVID-19. Within 19 days after symptom onset, 100% of patients tested positive for antiviral immunoglobulin-G (IgG). Seroconversion for IgG and IgM occurred simultaneously or sequentially. Both IgG and IgM titers plateaued within 6 days after seroconversion. Serological testing may be helpful for the diagnosis of suspected patients with negative RT–PCR results and for the identification of asymptomatic infections.