A: Immune memory to SARS-CoV-2 appears to last *at least* 8 months.
👉 TL;DR: While individual immunity levels varied, so far antibodies and immune cells specific for SARS-CoV-2 were detected up to 8 months later in 95% of patients who recovered from COVID19.
👍🏽Immunity to infection:
The immune system retains memory of a virus after recovering from infection with the specific virus. The immune system does this by making T and B cells that remember the virus and remain in our bodies for relatively long periods of time. When these cells encounter the specific virus again, they can quickly increase in number, make antibodies and other types of proteins that are necessary to clear the infection. In some cases, such as measles, we develop immune memory that can last us a lifetime. In other cases, such as the flu, our immune memory to this year’s flu variant does not recognize next year’s variant as robustly, because the two variants might be sufficiently different from each other, which is why we need an annual flu shot.
❓Why do we develop robust immune memory to some viruses and not others?
Immune memory for viruses that don’t mutate (change their genes) easily tends to be long lasting. In fact, a 2007 study found that it would take greater than 200 years for all the antibodies to the measles and mumps viruses to disappear completely after an infection! In contrast, the flu virus mutates very frequently. Therefore, the immune memory that we made to last year’s flu virus is not a good enough match to combat this year’s variant of the flu virus.
❓Where does SARS-CoV-2 fit? Do we have good immune memory after recovery from COVID19?
It’s still early days, as we only identified the first COVID-19 patients a little over a year ago. Testing for COVID19 antibodies and other measures of the immune response has also been available for less than a year. The good news is that much of the data suggest that most recovered from COVID19 patients make antibodies that can neutralize the virus. Researchers at the La Jolla Institute for Immunology found that 95% of people in their study had good immune memory for SARS-CoV-2 up to 8 months following recovery. B cells, the cells that make antibodies, actually increased in the blood of these people over time. SARS-CoV-2-specific T cells were also found to persist out to 8 months following infection. Although the amount of SARS-CoV-2 antibodies produced correlates with severity of infection, researchers have found that good immune memory also develops after mild COVID19.
Researchers have found immune cells to SARS (a coronavirus that is very similar to the SARS-CoV-2 virus) in patients who were infected with this virus over 15 years ago. In contrast, immune memory to the four ‘common cold’ causing coronaviruses doesn’t last very long, which is why we tend to catch colds every year.
❓So, will SARS-CoV-2 immune memory be more like that of SARS or the 4 common cold coronaviruses?
We don’t know the answer yet. Researchers are continuing to study the duration of the immune response to SARS-CoV-2, but we simply must wait for data to accumulate. As the intent of vaccination is to help the immune system develop memory for the virus, vaccine induced immunity to SARS-CoV-2 appears to be stronger and more consistent than natural infection. Previously infected individuals get a very strong immune boost from the first shot of the vaccine, so vaccination is recommended for all regardless of infection status (see recent post).
Both Pfizer and Moderna recently released data showing good protection *at least* 6 months from their vaccines (see recent post).
The new variants add a wrinkle to estimating the duration of immunity, which is why booster shots are being developed. New variants arise during periods of high transmission because the virus has lots of chances to replicate and make mistakes, some of which will help its chances of survival. In a world where transmission is low, new variants should be less common and our existing immunity more durable and effective. 🤞🏽
So far immune memory to SARS-CoV-2 is looking good. The immune system has many tricks up its sleeve including antibodies, memory B cells, and T cells.
Stay tuned for updates!
Those Nerdy Girls
📚 Further Reading:
More information on COVID19 vaccines and antibodies: