You may have seen a lot of press coverage today about the REACT study from @imperialcollege looking at SARS-CoV-2 antibody levels in the population...

A thread...

This study measures antibody levels against SARS2 in 365,000 people between 20th June and 28th Sept.
Initially 6% had antibodies to SARS2. That fell to 4.4%

Really interestingly they did not see a drop in antibody levels of healthcare workers. This might show that initial high exposure to the virus, or repeated exposure, prevents antibody levels falling to below the detectable limit as quickly.

Another important point is that 30% of people with antibodies had no history of COVID symptoms. These are likely very mild or asymptomatic infections. The decline in antibodies was largest in this group. They may not have had a robust immune response to the virus.

This waning of antibodies isn’t surprising. Seasonal coronaviruses are similar and show declining immunity over 6 months to a year.
Infection with other viruses, like flu, rhinovirus and measles results in antibodies that can be detected for years.

We do not yet know the implications of decreasing antibody levels on long term immunity. And it’s important to consider other aspects of the immune system.

There are two types of lymphocytes: B cells, which make antibodies and T cells, which can kill infected cells.
Our bodies can create memory B or T cells which can remember a virus.

If memory B or T cells are made it means the body can mount an immune response much faster the second time the virus is encountered.
We don’t yet know if COVID produces good memory cells.
Vaccines can help make these cells.

There is still a lot of work to be done to determine how long lasting immunity is to SARS2. We need to remember this virus has only been around for 11 months. It’s still very early days.

The immune system is so incredibly complicated that understanding it is an ongoing process.