The conversationJune 18, 2021 3:37:48 PM IS
With the acceleration of the launch of COVID-19 vaccines, more and more people ask which vaccine is the best?
Even if we tried to answer this question, defining which vaccine is the “best” is not straightforward. Does that mean the vaccine protects you better from serious diseases? The one that protects you from any variant that is circulating near you? The one that needs the least booster dose? The one in your age group? Or is it another measure entirely?
Even if we could define what is “best”, it is not like you have a vaccine option. Until a vaccine set is available, the vast majority of people around the world will be vaccinated with whatever vaccine is available. That is based on available clinical data and recommendations from health authorities, or what your doctor advises if you have an underlying medical condition. So the honest answer to which COVID vaccine is the “best” is simply the one that is available to you right now.
Still not convinced? Here’s why comparing COVID vaccines is so difficult.
Results from clinical trials only go so far
You might think that clinical trials might provide some answers on which vaccine is the “best”, particularly the large phase 3 trials that are used as the basis for approval by regulatory authorities around the world.
These trials, usually in tens of thousands of people, compare the number of COVID-19 cases in people who receive the vaccine to those who receive a placebo. This gives a measure of efficacy, or how well the vaccine works under the strictly controlled conditions of a clinical trial.
And we know that the efficacy of different COVID vaccines differs. For example, we learned from clinical trials that the Pfizer vaccine reported on 95 percent efficiency in the prevention of symptoms, while AstraZeneca had an efficacy of 62-90 percent, depending on the dosage regimen.
But the direct comparison of phase 3 trials is complex since they take place in different places and times. This means that infection rates in the community, public health measures, and the mix of different viral variants can vary. Trial participants may also differ in age, ethnicity, and possible underlying medical conditions.
We could compare vaccines face to face
One way to directly compare the effectiveness of vaccines is to conduct comparative studies. These compare the results of people who received one vaccine with those who received another, in the same trial.
In these trials, the way we measure efficacy, study population, and all other factors is the same. Therefore, we know that any difference in results must be due to differences between vaccines.
How about in the real world?
Until we wait for the results of comparative studies, we can learn a lot about how vaccines work in the wider community, outside of clinical trials. Real-world data tells us about the effectiveness of the vaccine (not about efficacy).
And the effectiveness of COVID vaccines can be compared in countries that have implemented different vaccines for the same populations.
For example, the latest data from the UK shows that both the Pfizer and AstraZeneca vaccines have similar effectiveness. They both reliably prevent COVID-19 symptoms, hospitalization and death, even after a single dose.
Therefore, what at first appears “better” based on the efficacy results of clinical trials does not always translate into the real world.
What about the future?
The COVID vaccine you receive today may not be the last. As immunity naturally wanes after immunization, periodic boosters will be necessary to maintain effective protection.
There is now promising data from Spain that combination and combination vaccines are safe and can trigger very powerful immune responses. Therefore, this may be a viable strategy to maintain high vaccine effectiveness over time.
In other words, the “best” vaccine could actually be several different vaccines.
Variant viruses have begun to circulate and, although current vaccines show reduced protection against these variants, they still protect.
So while a vaccine might be more effective in a phase 3 trial, that vaccine might not necessarily be the “best” one to protect against future variants of concern circulating near you.
The best vaccine is the one you can get now.
It is completely rational to want the “best” vaccine available. But the best vaccine is the one you have available at the moment because it prevents you from contracting COVID-19, reduces transmission vulnerable members of our community and substantially reduces their risk of serious illness.
All available vaccines do this job and do it well. From a collective perspective, these benefits are compounded. The more people vaccinated, the more immune the community becomes (also known as herd immunity), further reducing the spread of COVID-19.
The global pandemic is a highly dynamic situation, with emerging viral variants of concern, uncertain global vaccine supply, irregular government action, and the potential for explosive outbreaks in many regions.
So waiting for the perfect vaccine is an unattainable ambition. Each vaccine administered is a small but significant step towards global normality.