Q and A with the experts: the science of vaccine hesitancy

Thursday, August 27, 2020

Portrait of Roderick SlavcevSchool of Pharmacy Professor Roderick Slavcev knows better than most how important vaccinations are – he’s currently developing a DNA-based vaccine for COVID-19.

We asked Professor Slavcev to explain the science of vaccine hesitancy. What happens if we have a vaccine for COVID-19, but people won’t use it?

Will a vaccine be effective if some people choose not to receive it?

In order for the vaccine to be effective, the vast majority of the population must be immunized. Vaccines serve to prevent infection and protect individuals against infection at the population level in order to lead to the eradication of disease. Viruses of course can mutate and evade immune responses, hence leading to yearly epidemics such as we see for influenza, and the requirement for yearly vaccines. Not all individuals can safely take a vaccine, largely depending on the type of vaccine (e.g. live attenuated) and as such may rely on herd immunity to eradicate the virus thereby protecting those that are susceptible from probability of infection. 

What percent of the population must be vaccinated to contain the spread of COVID-19?

According to public health experts at least 70 per cent of the population, perhaps higher, will need to develop immunity to the COVID-19 virus to achieve herd immunity. Herd immunity is the population’s resistance to infection spread due to a vast majority of infections occurring in vaccinated individuals which rapidly clear the infection and prevent spread. What percent of the population is required to be vaccinated to acquire herd immunity varies by disease and can be over 90 per cent in some cases. Herd immunity relates to the ability of immunized and hence, individuals within the community that are immune to the disease, to protect non-immunized individuals within the population, by virtue of blocking the spread of infection to those are susceptible.

Why do some people decide not to be vaccinated?

The value of vaccines is difficult to appreciate in that when they are working effectively, no one notices a change. And yet, these preventative medicines are arguably among the most, if not most, important health technologies within our arsenal, at least on par with antibiotics. 

It is a fact that without them, our quality of life today would be vastly different and our historical path in confronting bacterial and viral diseases such as tuberculosis and smallpox would look very different today. But we don’t have that alternate dimension to offer as proof of value and the prevention of a pandemic is very difficult to appreciate when the devastating effects are not actually witnessed. Moreover, during normal periods of no public health emergency, our therapeutic focus is on precision and personalized medicine – co-creation of value with the patient in their own therapy – which is turned on its head during a pandemic where utilitarian approaches to public health must be adopted and personalized medicine is put on hold. 

Evidence of this confused juxtaposition can be seen by individuals that believe it is their personal right not to wear a mask, or more pertinently, refuse a vaccine despite the weakness this puts in the ‘protective armour’ of the population as a whole. If current polls are accurate in assuming that 16 per cent are ‘anti-vaxxers’ and another 19 per cent do not identify as ‘anti-vaxxers’ but refuse the vaccine for other reasons then it would appear that we will miss the minimal 70 per cent mark and fail to reach the threshold to eradicate COVID-19.

Will a vaccine be safe for children?

Vaccines come in a variety of types and strategies. They can be a subunit protein of the virus, a whole killed virus, or a live attenuated virus that has been ‘crippled’ to limit infection, virus-like particles that lack genetic material, or (as in our case) a nucleic acid vaccine that encodes protective viral components. 

Our youngest and oldest portions of the population are not as immunocompetent as the middle demographic and as such some vaccines are too dangerous to use in these populations. For instance, live attenuated viruses that are capable of replicating (albeit poorly) are not safe in children or a geriatric population while a subunit vaccine may be safe for the vast majority. 

It is important to note that all vaccines have to be approved by a regulatory body (Health Canada in Canada; FDA in USA) that determines the age demographic for which a released vaccine is safe. Safety and segment decisions are based on rigorous testing and data collected during preclinical and clinical trials. Furthermore, children’s vaccines are approved independently of adult versions requiring additional scrutiny.