There have been warnings from doctors and the UK’s Health Security Agency that falling immunity is causing death even in people who have received two doses of a Covid vaccine. So how much protection do we have left?
Let’s nail down some basics. The immune system has two major jobs – preventing us from becoming infected and, when that fails, ridding our body of infection.
I want you to use your imagination and imagine your immune system as a medieval castle.
The castle is surrounded by a hostile and ruthless coronavirus army desperately trying to get in.
Your first defense is an outer wall guarded by a legion of archers. These are your body’s neutralizing antibodies. If they can fend off the virus army, you won’t get infected.
But when the walls come down and the antibody archers leave, the virus is in. It stormed the castle and now you have an infection.
But all is not lost yet. There are still troops in the fortified keep at the heart of the castle. These are your memory B and memory T cells. Like mounted knights, they can rally the troops, lead the immunological attack, and route the enemy invaders.
The Covid vaccines have trained your body’s troops – which include both antibodies and those memory cells that respond to infection – to take on the coronavirus.
At least one of those defenders is dwindling, and that’s no surprise. This happens after every vaccination or infection.
‘There is good evidence that antibodies wane over time and that has left us with obvious flaws,’ says Prof Eleanor Riley, an immunologist from the University of Edinburgh.
The desertion of these Antibody Archers from their posts has been made worse by the appearance of the Delta variant. It’s just better at spreading out and invading our bodies – it’s like a new army bouncing outside the walls, but this one brought a cave troll and siege weapons.
You may have noticed the consequences of this yourself – people you know who have been double-vaccinated but have contracted Covid anyway. Research that has not been officially released estimates that the AstraZeneca vaccine reduced any form of Covid symptoms by 66% shortly after the second dose. Five months later, that number had fallen to 47%. At Pfizer, the numbers dropped from 90% to 70%.
This is obviously a problem for governments trying to contain the spread of the virus. Whether the virus invasion will do any serious damage as it tries to weave and plunder its way through your body now depends on your second line of defense. However, the vaccines are now keeping fewer people out of the hospital.
Prof Adam Finn, from the University of Bristol and government vaccination adviser, says: “We are seeing a significant number of unvaccinated and vaccinated people coming into hospital.
“The protection you have from a relatively mild infection wears off faster, but the protection you have from being hospitalized or killing you wears off more slowly.”
The higher risk of being treated in hospital or even dying is concentrated in older people. The overwhelming majority of deaths among those who were double-vaccinated were among those over 70 years of age. People in this age group are still doing far better than someone they share a birthday with but have declined the vaccine. And as you can see, the risks are small in younger age groups who have been double-vaccinated.
The constant rush of time ages every cell in our body—including those that make up the immune system. With age, the immune system becomes more difficult to train with vaccines and is slower to respond when infection occurs. It may be that the antibodies have now dropped far enough that this weakness in the immune system is being revealed.
“It’s possible that older people initially had protection, but now those antibodies are weakened, they may not have the second line of defense anymore,” says Prof. Eleanor Riley.
“That could be why we’re seeing elderly, frail people dying despite two doses.”
All of this is overlaid by the fact that aging tends to be associated with disease. Since the pandemic began, age has been one of the biggest factors in how likely you are to die from it. The oldest people were also the first to be vaccinated, giving their immunity more time to wear off.
People who start out with a weakened immune system, including cancer and organ transplant patients, have a subtly different problem, as their bodies don’t respond as well to vaccines.
“Their antibodies decrease at a rate similar to that of healthy people, but they obviously start at a lower point,” says Dr. Helen Parry from the University of Birmingham
It’s worth noting that there are important differences between the Oxford-AstraZeneca and Pfizer-BioNTech vaccines, which have done most of the work to protect people in the UK.
“They seem to be good in different parts of the immune system,” says Dr. parry
“The mRNA vaccines (Pfizer) are really good at generating antibodies, the AstraZeneca vaccine is really good at generating T-cell responses.”
To get back to the castle, Pfizer might be better at garrisoning the outer walls with archers to keep Covid out, while AstraZeneca is good for the inner keep.
The good news is that even as vaccination wanes, these are still exceptionally good vaccines. At the beginning of the pandemic, people dreamed of a vaccine that could cut deaths by 50%. Even as it decreases and in the most vulnerable age groups, this protection is still in the 80-90% range.
“Even the worst cases, six months later, are better than what we had hoped for when developing these vaccines,” says Prof. Finn. “They are still very good.”
The even better news is that there is already evidence that the Booster campaign – which has reached more than 11 million people in the UK – is making a difference. Data from the Office for National Statistics show that levels of antibodies – those first defenders against infection – have risen again in the oldest age groups.
“Giving the elders a booster shot is a hit,” says Prof. Finn.
Everyone is now watching the numbers closely to see if that brings down the number of cases and deaths.
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