Why Can’t the Covid-19 Vaccine Provide 100% Protection?

As you may have heard or seen from the news and in the papers, yes, the Covid-19 vaccine is indeed not impenetrable as we had all desperately hoped. This means the vaccine is not able to offer full or immediate protection.

Here are some plausible reasons why vaccines are not meant to offer 100 per cent protection.

How do vaccines work?

First up, let us understand how vaccines work.

Vaccines contain inactive or weakened parts of antigen which triggers an immune response in our bodies. When the immune response is awakened, two important types of white blood cells – Plasma B cells and T cells – are activated.

The main function of the Plasma B cells is in making antibodies. Alas, these cells are short-lived and the number of antibodies produced will see a rapid decline without the second shot of vaccine. With the second dose, Plasma B cells enter a maturation stage and get multiplied to produce better-targeted antibodies.

Karolina Grabowska/Pexels

Next, we have the T cells which can identify a particular pathogen to eliminate it. Its sub-part, Memory T cells, have an even longer lifespan and can linger in the body for decades until it finds its target. These particular cells proliferate expeditiously and are presumed to be playing a critical role in fighting the current pandemic.

This goes to show that the immunity brought upon by vaccines can last up to a lifetime.

READ: Side Effects of COVID-19 Vaccine: Should We Be Concerned?

1. Immunity takes time to develop

Edward Jenner/Pexels

Time is one of the reasons why some people still tested positive after two doses of vaccine.

For vaccines to properly work its magic, the body must first make more immune cells which require time to develop. The Covid-19 vaccines being used in Singapore warrants two doses, given weeks or months apart. With the second dose, protection against diseases is almost doubled. Not taking the second dose will bring an individual’s immunity level back to square one.

As time passes by, our bodies will generate higher counts of long-lived antibodies and memory cells to rapidly fight the virus, should an individual ever encounter it.

2. Vaccines do not work retroactively


Vaccines are not meant to undo a disease or infection, but what it can do is prevent the body from contracting viruses such as Covid-19. Cases where a person tested positive after receiving vaccines are because they were already infected prior to their first dose. Since vaccines are not built to work retroactively, it cannot retract the virus from the individual.

Out of 4,081 American health care workers, 22 tested positive for Covid-19 after being vaccinated, in a study conducted by the US Centers for Disease Control and Prevention.

However, researchers believe that a person is less likely to fall sick when vaccinated and have lesser chances of contracting Covid-19.

READ: Busting Covid-19 Vaccine Myths

+ HSA grants interim authorisation for the Moderna’s vaccine in Singapore

The second addition to the line of Covid-19 vaccinations used in Singapore, Moderna, will be made available for individuals aged 18 and above. The Moderna vaccine will require two doses to be administered, 28 days apart.

Based off available clinical data, Moderna’s benefits outweigh the known risks with a high vaccine efficacy of 94 per cent. The Health Sciences Authority (HSA) will continue to “actively review” data to make sure the benefits continue to outweigh the risks identified. 

As more Pfizer-BioNTech and Moderna vaccines are expected to arrive throughout the year, sufficient supply is expected for all Singaporeans and long-term residents by Q3 2021.

Charlie Ridel/AP Photo

While we still have not found a foolproof cure for Covid-19, what we can do for now is to make good use of the available resources to combat the virus. Continue taking care of your personal hygiene, keep your hand soaps and sanitisers handy, have your masks on at all times and maintain social distancing. With joint community effort and perseverance, we will soon get to live in a pandemic-free world again!

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