The ability to prevent the spread of SARS-CoV-2, the virus that causes COVID-19, through vaccination depends on how infectious the virus is, the uptake of vaccination, and how effective the vaccine is at preventing infection.
No data is available on how effective the Pfizer vaccine is at preventing infection entirely, although it’s expected to more than halve the risk of infection, based on data from another mRNA vaccine from Moderna. There is preliminary data from the AstraZeneca vaccine on the prevention of infection, and like the Moderna vaccine, it also indicates a reduced risk.
This is great news, as many expected none of the COVID-19 vaccines would have a major impact in terms of providing sterilising immunity – complete protection against infection. But the argument that mRNA vaccines such as Pfizer and Moderna will lift Australia to the nirvana of COVID-19 herd immunity while reliance on AstraZeneca will impede such a goal is flawed.
Herd immunity may not be achievable with any vaccine, and even if achieved may not be sustained. A more likely scenario, even if the Pfizer vaccine alone is used, is that there will be some ongoing infection among the non-vaccinated and that some vaccinated people will still get sick, but there will be very few cases of severe COVID-19 and very few deaths.
A recent modelling study in the journal Science indicated that vaccination will most likely shift SARS-CoV-2 from a virus that causes major COVID-19 disease burden to an endemic, relatively benign coronavirus such as the several that already circulate, causing the common cold. This is a good outcome. How quickly we can reach this goal depends directly on how rapidly we can roll out vaccines. That is why we need to have AstraZeneca in the mix.
The Australian government’s COVID-19 vaccine strategy is to start vaccinating people in February, once the Therapeutic Goods Administration has evaluated the safety and efficacy data for the vaccine candidates and approved (as expected) their use. The Pfizer vaccine will probably be approved first, then AstraZeneca. The initial groups vaccinated will include quarantine and border workers, front-line healthcare workers, and aged care and disability care staff and residents.
This will be followed by the elderly and other vulnerable populations. Contracts are in place with Pfizer (10 million doses), AstraZeneca (54 million doses), and another promising vaccine from Novavax (50 million doses).
The vaccine issue that really needs our attention is the timeline for rollout completion. The goal is October, but this needs to be accelerated, and certainly not delayed by argument about AstraZeneca. Completion by winter would greatly limit the risk of a major COVID-19 burden such as that being experienced by most countries in the northern hemisphere.
Once the vaccines are approved, I will be more than happy to receive either the Pfizer or AstraZeneca vaccine, particularly if they are part of an accelerated program that pushes us further along the pathway to COVID “after times”.
The overall COVID-19 strategy in Australia should be to allow us to move from an elimination-type strategy to a vaccination/protection strategy that requires only limited, if any, restrictions like lockdowns. Such a goal is achievable during 2021, particularly if there are no pauses placed on a vaccine rollout that none could have envisaged a year ago.
Professor Gregory Dore is an infectious diseases physician and epidemiologist at the Kirby Institute, UNSW Sydney.