Some COVID-19 variants can break through the vaccine defense and even vaccinated people can get sick.
But there is another line of defense, called killer T cells, and they prevent vaccinated people from getting seriously ill, going to the hospital or dying.
The new kinds of vaccines – those that use mRNA, like Moderna and Pfizer-BioNTech, or viral vectors, like Oxford-AstraZeneca – they are really good at this.
To understand why, let’s look at how most vaccines work.
The Sinopharm and Sinovac vaccines are typical of the old kind. They work by injecting a dead virus.
Part of your immune system responds to it by making antibodies against many areas of the dead virus.
The best ones are the ones that stick to a specific part of the virus – the part that it uses to get into your cells.
They are called neutralizing antibodies. When the real virus comes, they will block it to start an infection.
But omicron is highly mutated. These neutralizing antibodies do not hold up so well.
The virus can enter your cells and start an infection.
Infection turns your cells into virus factories. They secrete more viruses, which infect more cells, which make more viruses and so on.
This is where killer T cells come in. These cells patrol the body, looking for and destroying infected cells.
Killing T cells knocks out virus factories.
So when antibodies do not prevent the virus from causing an infection, killer T cells prevent it from getting out of control.
The new vaccines are good for recruiting killer T cells because they work differently than old vaccines. Here’s how you do it.
Do you remember how the old vaccines inject a dead virus? Well, the new ones are injecting genetic instructions to make a piece of that virus.
Your cells take the instructions and make the virus piece themselves.
It’s a bit like what the virus does – turning your cells into virus factories. But these pieces of virus do no harm.
What they do is train T cells to recognize infected cells.
Meanwhile, the part of the immune system that makes antibodies also gets started with these pieces of virus.
So while the old vaccines mostly made antibodies, the new ones put two branches of the immune system to work for you: antibodies and T cells.
So if a mutated virus gets past the antibodies and starts an infection, killer T cells will usually prevent it from becoming serious.
The new mRNA vaccines are good for recruiting T cells. These are the Moderna and Pfizer BioNTech images.
The viral vector vaccines from Oxford-AstraZeneca, Johnson & Johnson and Sputnik V do this too.
These hold up against variants. People who received these vaccines get breakthrough infections, but for the most part, they do not become seriously ill or dying. These new kinds of vaccines really help.