Fears that our immune system could quickly forget the encounter with the SARS-CoV-2 virus are increasingly unfounded, an Australian study revealing our blood is still able to provide a strong response eight months after infection.
This is good news for those concerned that COVID-19 vaccines will not provide the protection period needed to manage the spread of the virus throughout the population.
“This has been a black cloud that hangs over the potential protection that could be provided by any COVID-19 vaccine and offers real hope that once a vaccine or vaccines are developed, they will provide long-term protection,” says the University immunologist. Monash Menno van Zelm.
Although it is still too early to say how long immunity to this specific coronavirus could last, we can be sure that time will probably be on our side.
In a collaboration between Monash University, Alfred Hospital and the Burnet Institute in Melbourne, the researchers analyzed blood samples taken from 25 volunteers diagnosed with COVID-19.
Each sample provided a snapshot of the condition of the immune system, from just four days after infection to eight months.
Another 36 people with no history of the disease also provided one or two blood samples for comparison.
COVID-positive evidence suggests that SARS-CoV-2 free floating antibody concentrations begin to fade just 20 days after symptoms occur, a finding that is consistent with previous studies suggesting that antibody levels decline rapidly, especially in mild cases of COVID-19.
Although this in itself is not surprising, it has caused consternation among immunologists if we should expect waves of reinfections in the coming years.
Antibodies are like shots for the immune system, allowing them to easily throw themselves on past criminals who dare to show their face again. Without them, it is far too easy for a past infection to return immediately.
In the case of pathogens, these “desired” chemical posters remain for years. Measles, for example, causes an antibody response that barely decreases throughout life.
Other disease agents fade out of memory a little faster. For tetanus, this disappearance lasts a little over a decade, requiring frequent reminders in the form of booster vaccines to push the system to reprint a fresh batch of antibodies.
The key to this antibody printing service is the white blood cells called memory B cells. Formed during an infection to print antibodies specific to an invader, these cells can hide for decades, once the heat goes out, ready to generate a new amount of antibodies at some point, if the pathogen reappears.
To see if a known immune system of COVID still had enough B cells to do the job after just a few months, the researchers inserted fluorescent-labeled pieces of SARS-CoV-2 into the once infected blood samples.
The analysis not only revealed a significant response in each of the COVID-19 blood samples, but allowed the team to determine what types of B memory cells react to which particular piece of the virus’s body.
“These results are important because they show that patients infected with the COVID-19 virus actually retain immunity to the virus and the disease,” says van Zelm.
And since the proteins analyzed in the study are considered the main target sites, we can expect most vaccines to also transmit a good level of immunity for at least eight months.
Beyond that? Time will tell. We hope that we will be able to bring news in the next years of continuous immunity, which lasts far beyond expectations.
For the pandemic to be brought under control well, if it is not completely eradicated, we will need at least 70% of the population to be immune in the same period of time. Only then can we be sure that the virus will have so few places to hide that it could disappear.
At this point we can be pretty sure that the window is eight months wide. Let’s hope that’s enough.
This research was published in Scientific immunology.