Vaccines have had a transformative impact on global public health. Despite many decades of progress, however, there remain important challenges associated with immunisation.
Determining whether a vaccine will be successful involves resolving important questions regarding vaccine effectiveness, distribution and uptake. There are currently at least seven COVID-19 vaccine candidates at the phase-three stage, which involves large-scale (30k-60k participants per candidate vaccine), randomised field trials designed to demonstrate efficacy. The headline number for the Pfizer vaccine efficacy is >90%, which reflects the fact that there were 94 cases in the trial population of >40,000 and of these 94 only 8 were in the group receiving the vaccine. The threshold set by the WHO is for 50% efficacy (typical of many flu vaccines).
Of course, there are still many further uncertainties, for example, whether the vaccine affects the ability to infect others as opposed to simply protecting the vaccinated person. Moreover, the percentage from vulnerable groups in the trial is not yet known and so it is unclear whether the vaccine is equally effective on the groups in greatest danger from COVID-19. There are also concerns that more details have not yet been made available.
Still, the Pfizer announcement is in itself is an important medical advance both because of its public health and economic benefits of treating COVID-19 and because this would be the first major mRNA (messenger RNA) vaccine. One challenge to supply chains specific to mRNA vaccines such as Pfizer and Moderna is that they require very low temperatures (-70C) and this will be challenging both in terms of having sufficient cryogenic storage across the supply chain but also in terms of training medical staff to administer a new type of vaccine. Aside from traditional concerns over equitable distribution, these technical challenges will make it difficult to bring this sort of vaccine to the countries with the weakest healthcare infrastructure.
Finally, all these trials are based on volunteers and any vaccine will need to be adopted by sufficient numbers within the population at large to produce the much-discussed herd immunity. Thus, the final remaining challenge is not a technical one but a question for social psychology. Virtually all major immunisation campaigns are aimed at infants and children and the experience with adult vaccination has been viewed as challenging. Indeed, just last year, the WHO named ‘vaccine hesitancy’ as one of the top ten global health threats. This vaccine hesitancy is related to the 3Cs:
- Complacency — the perception of low risk or low value from the vaccine
- Confidence — concerns about the safety of vaccines and those who administer them, or more broadly a lack of trust.
- Convenience — where access to services is difficult.
What do you see as the biggest barriers to widespread vaccination and how might such barriers be overcome?
P.S. Don’t forget to fill out the Twitter poll (it expires on Sunday evening since some of you wanted to find out what others thought before blogging your response!)