US President Joe Biden says coronavirus booster shots will be available for people eight months after they received their second shot of the vaccine. Video / AP
Anyone keeping an eye on coronavirus antibody levels in Britain may have noticed an alarming trend in recent months.
Since peaking in May, the percentage of older people who are testing positive for protective antibodies has been steadily declining. It rose to 95 per cent for the over-80s, and has now fallen to 92.4.
In fact, only the under-50s are not seeing a drop in antibody levels, according to the Office for National Statistics (ONS).
This signal of waning immunity has led to calls for booster jabs ahead of a winter wave.
But several studies have come out in the last few months that suggest we might not need to be too worried after all. Antibodies are not the only indicator of immunity.
In May, researchers at Washington University School of Medicine, who studied 77 recovering Covid patients, found that while antibodies declined over time, bone marrow plasma cells - capable of producing antibodies against the virus - remained stable.
Dialled-down protection could last a lifetime
It means that people who have recovered from an infection have immunity hidden away in their bones ready to spring into action. This type of dialled-down protection could last decades, or even a lifetime, the researchers believe.
The team also found patients were carrying memory B-cells - a type of white blood cell - which patrols the blood looking for the virus.
A security staffer directs traffic at a Covid-19 mass vaccination event at Auckland Airport on Sunday. Photo / Dean Purcell
In fact, the researchers noted that the levels of B-cells found in recovered Covid-19 patients are equal to people vaccinated against tetanus or diphtheria, both vaccines that provide long-term immunity to those diseases.
Similarly, researchers from The Rockefeller University, New York, recently found that recovered Covid patients still have immunity a year after infection, including antibodies that were "exceptionally resistant" to variants.
"The data suggest that immunity in convalescent individuals will be very long-lasting and that convalescent individuals who receive available mRNA vaccines will produce antibodies and memory B-cells that should be protective against circulating SARS-CoV-2 variants," the researchers concluded.
The problem with only looking at antibodies is it gives a false picture of the level of protection. The body is efficient, and will not continue to produce high levels of antibodies when they are no longer needed.
Blueprints for making antibodies are squirrelled away
This is a good thing, as it prevents the onset of auto-immunity, which can lead to a slew of debilitating conditions. Instead, the blueprints for making antibodies are squirrelled away, while a casual surveillance is mounted by the immune system.
But bone marrow and B-cells are not all the body has stashed away for a future fight. Last year, Imperial College found that people who had recovered from Covid still had memory T-cells even after antibodies had waned.
T-cells are a kind of white blood cell which stores the details of a past infection and can quickly multiply on re-exposure, providing a rapid response to an invader.
T-cells may also have the added benefit of being able to fight variants. While antibodies only detect proteins on the outside of cells, such as the spike protein which the virus uses to latch on to human cells, T-cells can hone in on proteins inside infected cells. Crucially, many of these do not change when the virus mutates.
Earlier this year, scientists at the La Jolla Institute for Immunology in California found that people infected by Covid generate T-cells that target at least 15 to 20 different fragments of coronavirus proteins, and would work even against worrying mutations such as the 501Y.V2 mutation found in the South Africa (Beta) variant.
Although there have been some breakthrough infections with the Delta variant, the vast majority (82%) of people catching Covid in the UK currently have not had two vaccine doses. Photo / AP
Infections from the original Sars virus have also produced immunity in recovered patients that have lasted decades. A study by scientists in Singapore, published last week, found that Sars patients who were vaccinated against Covid produced high levels of neutralising antibodies against both viruses.
It suggests that memory regions of the immune system were jogged into action by the vaccine, raising hope that coronavirus infection or vaccination offers long-term protection which can be easily ramped up if the virus re-emerges.
Certainly we are not seeing any indication that vaccinated people are becoming more at risk for reinfection. Although there have been some breakthrough infections with the Delta variant, the vast majority (82 per cent) of people catching Covid currently have not had two doses.
The UK's Joint Committee on Vaccination and Immunisation (JCVI) is expected to advise that booster vaccinations will not be rolled out to the wider population, although some more vulnerable people may be offered a third jab. For most of us, it is likely we will be safe enough with just two.
