Scientists across the world are working around the clock to develop vaccines against SARS-CoV-2, the virus which is responsible for the COVID-19 global pandemic. Although therapies such as Gilead’s newly approved antiviral drug Remdesivir and repurposed decades-old steroid dexamethasone have shown to have some positive impacts against the severity of the disease, a safe and efficacious vaccine is still the best hope for ending the pandemic and returning society to normal.
There are a number of promising vaccine candidates, some of which could lead to vaccines being available as early as the end of this year in our opinion. The implications for our societies, economies and investments could not be greater. That is why we would like to offer an overview of the current efforts and their likelihood of success based on our background and experience in healthcare analysis and immunology. Few of us are epidemiologists or immunologists so we would like to start with basic definitions before discussing the different vaccine candidates in detail.
How does a vaccine work?
To understand how vaccines work, let us first look at how our immune system works. When a harmful bacteria/virus enters our body, our immune system quickly recognises it as an invader. It triggers a complex chain of reaction involving many white blood cells (Macrophages, B-lymphocytes and T-lymphocytes) working together to fight off infection. One type of white cell (B-lymphocytes) can make antibodies whose shape has the exact fit to the surface of bacteria/virus like a key (antibody) to a lock (antigen). It takes several days for our body to produce the ‘key’ (antibody) giving the bacteria/virus time to replicate within our body and possibly make us ill. Once our antibody production factory is fully online and antibodies start to kill bacteria/virus, most of us get better. Our immune system remembers what it learnt about how to protect our body after the recovery and some white cells (T-lymphocytes) have memory and can go into action quickly if we encounter the same bacteria/virus again. B-lymphocytes, which produce antibodies, attack the invaders and protect us from getting ill the next time round.
Vaccines work the same way. They contain weakened or dead bacteria/virus, fragment or a genetic coding of it. They help to develop immunity by imitating an infection but without causing the disease. Our immune system responds as if the real invader has got in and produces T-lymphocytes and antibodies. Sometimes, the imitation infection can cause minor symptoms which is normal as our body builds up its immunity. Once the imitation infection has gone away, our body is left with memory T-lymphocytes as well as B-Lymphocytes that remember how to fight the disease in future.
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