COVID-19: Vaccines, Herd Immunity, What’s it All About?

by Dr Makini McGuire-Brown

I think everyone has come to terms with the fact that the novel Coronavirus is here to stay for a long time (and if you haven’t, you need to accept it). As restrictions continue in various forms and as countries cycle through re-opening and closing back down again, people must be wondering when and if this will ever end. End really means that we live with the virus’s existence without the level of morbidity and mortality of present. To achieve this, a significant proportion of the population has to become immune. In theory there are 2 routes to this: vaccination or herd immunity. In this article I’ll explain these two and put it into the COVID-19 context. First though we start with a crash course in the immune system.  

Our immune system is complex and fantastic. Not only does it contain cells that actively fight the offending organisms, like viruses, but it also contains memory cells that remember the offender, thereby allowing for a fast and effective attack and annihilation the next time the same offender tries to get you sick. To accomplish this a few different types of specialised cells have to recognise the foreign offender, recruit the fighters to beat the current infection, present an identifier of the offender to the memory cells and then the much talked about and famous antibodies are formed.

This again is broken into phases. The first set of antibodies are involved in the present infection while the follow up antibodies exist to mount the annihilation if the offender returns. Under ideal conditions such as a healthy immune system, ‘forever’ antibodies  and a stable offender, the exact offender cannot get you sick twice. However, ideal is not a luxury that we frequently have. While we have effective vaccination and organic immunity to viruses like chickenpox and it is extremely rare to get a repeat infection, the seasonal flu changes strains regularly and so new vaccines are created every year.

Currently everyone is on the edge of their seat awaiting a vaccine and thousands of professionals around the world are working on one. So what do vaccines do? Vaccines trick the body into thinking that it has been infected and trigger it to mount the immune response. Various types of vaccines do this in different ways but the objective is the same: trigger the immune response sufficiently so that antibodies are created against the offender. In this way an effective vaccines grants immunity to a specific virus. How long immunity lasts varies which is why some vaccines are single dose whereas others require booster shots or like the flu vaccine, need to be taken annually.

Of course while we wait for an effective vaccine which can take anywhere from long to never going to happen, we remain under restrictions. Many people are unwilling or unable to adapt and others still in the medical community campaign for a different approach to immunity; herd immunity. The concept of herd immunity means that we allow a significant (calculated using various models) number of people to contract the virus, develop antibodies and therefore we have eliminated them as possible transmitters and carriers because they supposedly cannot get infected again. This therefore would decrease spread and stem the pandemic. While the problem with vaccines is the length of time they take to develop, the problem with herd immunity is the risk of morbidity and mortality. As we have seen, COVID-19 sometime leads to death.

In the context of COVID-19, here’s what we know so far. Most people who have had the illness tested positive for antibodies but there is a lot of doubt surrounding the longevity of the antibodies, they seem to be waning a few months out. This is unfortunate as it makes an effective vaccine more difficult to come by and extends the time to attain it. It also increases the risk of aiming for herd immunity and makes it almost elusive as the same people can become sick repeatedly and therefore they remain transmitters.

It’s a long road ahead and it may seem hopeless but this too shall pass. We must remember that there is no perfect answer to managing a pandemic. I hope that through this article you get a greater appreciation of the difficult decisions being made.

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