Fears that our immune system could soon forget the encounter with the SARS-CoV-2 virus is becoming increasingly unfounded, with an Australian study revealing that eight months after infection, our blood is still capable of producing a strong build response.
This is good news for those concerned that COVID-19 vaccines will not provide the period of protection necessary to control the spread of the virus through the population.
“This has been a black cloud hovering over the potential protection that any COVID-19 vaccine could provide and gives real hope that once a vaccine or vaccines are developed they will provide long-term protection,” said Monash University immunologist Menno. van Zelm.
While it’s too early to say how long immunity to this particular coronavirus could last, we can rest assured that time will likely be on our side.
In a collaboration between Monash University, The Alfred Hospital and the Burnet Institute in Melbourne, researchers analyzed blood samples from 25 volunteers diagnosed with COVID-19.
Each sample provided a snapshot of immune system status from as little as four days after infection to as long as eight months.
Another 36 subjects with no history of the disease also provided one or two blood samples for comparison.
The COVID-positive samples suggest that levels of free-floating SARS-CoV-2 antibodies begin to fade just 20 days after symptoms appear, a finding consistent with previous studies suggesting that antibody levels fall rapidly, especially in mild cases from COVID-19.
While this in itself is not surprising, it has sparked concern among immunologists about whether we should expect waves of re-infections in the coming years.
Antibodies are like mug shots to the immune system, making it easy to attack past perpetrators who dare to show their faces. Without them, it’s far too easy for a past infection to roll back into it.
In the case of some pathogens, these chemical ‘wanted’ posters stick around for years. Measles, for example, causes an antibody response that barely diminishes during your lifetime.
Other pathogens disappear from the memory a little faster. For tetanus, this disappearance lasts a little over a decade, requiring frequent reminders in the form of booster vaccines to prompt the system to print another batch of antibody ‘mug shots’.
The key to this antibody printing service are white blood cells called memory B cells. Formed during an infection to print antibodies specific to an invader, these cells can hide for decades as the heat subsides, ready to generate a new supply of antibodies in an instant should the pathogen reappear.
To see if a COVID-known immune system still had enough B cells to do the job after just a few months, the researchers introduced fluorescently 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 also enabled the team to determine which types of B memory cells responded to which specific part of the body of the virus.
“These results are important because they definitively demonstrate that patients infected with the COVID-19 virus do indeed retain immunity to the virus and disease,” says van Zelm.
And since the proteins analyzed by the study are considered the major target sites, we can expect that most vaccines will also transmit good levels of immunity for at least eight months.
Beyond that? Time will tell. Hopefully, in the coming years we can bring news of ongoing immunity that remains far above expectations.
In order to properly control, if not completely eradicate, the pandemic, we need at least 70 percent of the population to be immune within the same time frame. Only then can we be sure that the virus has so few places to hide that it might disappear.
At this point, we can be pretty sure that this window is eight months wide. Let’s hope it is enough.
This research is published in Science Immunology.