By Corina Tan
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As we move into an endemic stage in our battle with Covid-19, we have started giving third booster shots to the frontline, elderly and immune-compromised. The healthy still wait anxiously for their turn, as cases seem to be climbing back up and ICUs begin to fill up yet again. There is increased talk about waning immunity as a whole and how the world is going to handle this predicament.
The immune system works by preventing us from getting infections and if that fails, and we still get an infection, it helps fight and clear the infection from our bodies. To understand how the covid vaccine works with our immunity to combat Covid-19, imagine your body surrounded by a fortress. Covid wants to invade your body, but your first defence is your body’s neutralising antibodies. If they can hold off the virus, then you won’t get infected. But if at this stage the fortress crumbles, then the virus gets in. You are now infected, but there are still troops on the inside to defend you. Once they recognize the invaders, they will call on other troops to fight together. These are what is called your memory T cells and B cells that are also part of your immune system.
Once you get both doses of the covid vaccine, it trains your antibodies as well as your immune system’s memory T cells and B cells to react to a Covid-19 infection. With time, at least one of these troops will be waning, as is what happens after every vaccine or infection. The consequence of this is seen in people who have had both vaccine doses but still contract Covid-19. This is obviously a major issue as we are trying to contain the spread of the virus. The emergence of the Delta variant, which is so much better at spreading and getting inside our bodies make this waning immunity a global concern.
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As time goes on, the vaccines are now keeping fewer people out of the hospital, which is why many countries have started giving a third and even fourth dose. Prof Adam Finn, from the University of Bristol and a government vaccine adviser says, “The protection you have against relatively mild infection wanes more quickly, but protection from getting into hospital or killing you wanes more slowly.” It remains a fact that the elderly are still at the greatest risk of needing hospital care or dying. Every cell in the body is affected by ageing, including the cells that make up the immune system. Getting older makes it harder to train the immune system with vaccines, as the response is slower due to ageing cells. Also, since the elderly were the first to be vaccinated, their immunity has had more time to wane.
For people who have low immunity due to auto-immune diseases, cancer and organ transplants, they experience a slightly different issue as their bodies do not respond as well to vaccines in the first place. While their antibodies wane at the same time as healthy people, they start off with lower immunity anyway, thus when whatever small percentage of immunity they have wanes, it leaves them with little to none to fight off the infection.
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We are now relying on the boosters to increase protection and get everyone back on track to a level that the immune system is strong enough to fight from the outside as well as the inside. Dr Helen Parry, from the University of Birmingham mentioned that different vaccines have shown to be good at different parts of the immune system. She said, “The mRNA vaccines like Pfizer are really potent at antibody formation, while AstraZeneca vaccine is really good at generating T-cell responses.”
In Malaysia, Health Minister Khairy Jamaluddin said the effectiveness of vaccines wane after a few months with Sinovac being the quickest to lose its effectiveness. “While Sinovac is effective, there is evidence its effectiveness wanes sooner. That’s why we want you to take whatever booster is on offer.” he tweeted on Saturday, November 20. He explained that the faster waning period is why Sinovac booster shots are three months, compared with six months for Pfizer and AstraZeneca. In his tweet, Khairy shared a graph showing data for Covid-19 admissions in Hospital Sungai Buloh in the state of Selangor. It revealed that most of Category 4 and 5 patients are Sinovac recipients.
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