Herd immunity is not the only goal of vaccinating Australians during the pandemic

Hassan Vally
·6 min read
<span>Photograph: Darrian Traynor/Getty Images</span>
Photograph: Darrian Traynor/Getty Images

Last week a controversy played out in the media regarding the vaccine strategy in Australia. This was as a result of calls to delay the AstraZeneca vaccine rollout because of the potential availability of other vaccines that have a higher vaccine efficacy.

While not discounting the importance of asking questions and raising concerns, it’s important to highlight that this call was driven by a misunderstanding of what we are aiming for in terms of a vaccine strategy in Australia in the context of a pandemic where infections are raging out of control in other parts of the world and vaccine supplies are limited.

It was also based on a number of false assumptions. Firstly, that achieving herd immunity – obtaining enough immunity in the population so that Covid transmission cannot take hold – is the only worthwhile goal of vaccinating the Australian population during the pandemic. And secondly, that achieving herd immunity for Covid with what we know about the vaccines currently available is simply a mathematical certainty if vaccine efficacy is high enough to allow the required threshold of immunity to be met in a population. Both of these assumptions were false.

Related: Coronavirus Australia live: three of four Covid-19 cases found in Victorian hotel quarantine linked to the Australian Open

Before addressing these assumptions separately, it’s also important to note that what got a bit lost in the controversy was how good our position is in Australia. If in January 2020, as the pandemic was taking off, you would have said that we would not only have one vaccine but many by January 2021, and not only would they all be safe and highly effective against disease, but they would be 100% effective against severe disease, most experts would have said, in the words of Dale Kerrigan, that you were dreaming. Remember, even having one vaccine represents a couple of medical firsts. It represents the first time we have ever successfully developed a vaccine to any coronavirus. It also is the first time we have developed and produced a vaccine of any type in under one year, and excitingly, by using two novel platforms which promise to revolutionise vaccine development more broadly into the future. That we have a number of vaccines available, and several others which will become available in the months ahead, is somewhat of a medical miracle that we should not lose sight of.

Returning to the false assumptions. The first assumption was that the only goal of the vaccine program in Australia is herd immunity. While there has been a lot of focus on herd immunity during the pandemic, and this is no doubt the long-term goal of the vaccine strategy in Australia, it’s important to make the distinction between what the long term goals are and what our more immediate goals are. The immediate goal of vaccine programs in all countries, including Australia, has to be to protect lives. Clearly, the urgency is different in countries depending on their current state of virus transmission. In Australia we are incredibly fortunate as we do not have the urgency that exists in many other countries.

In the matter of saving lives, it bears repeating that all of the vaccine options that we have are 100% effective in protecting against severe disease. What that means is that based on publicly available data from phase three trials, if you are vaccinated you will not have severe disease, you will not have to be hospitalised, and you will not die. To put this in perspective, if the vulnerable groups in Victoria during the second wave were vaccinated with any of the vaccine options we have available to us, potentially all of the lives lost during this wave would have been saved. The point here is that the only way to protect the community is to make sure that whatever vaccines that we actually have access to are delivered to the population. Subsequent waves of disease are an ever present threat in Australia, as they are in other countries, and so we need to do everything to protect the health of people in the event of this possibility.

The second assumption that fuelled the controversy was that our ability to develop herd immunity with the vaccines we currently have is a mathematical certainty given high enough efficacy of the vaccine and sufficient vaccine coverage. This assumption also does not hold. There are other factors that need to be considered in achieving herd immunity. Most importantly, we don’t have good data on to what extent the vaccines prevent infection rather than just clinical illness, and this is a key requirement to developing herd immunity. We also don’t have good data on how long immunity will last with any of the vaccines, which makes sense since we need to have followed people over time to answer this question, and we have not had the opportunity to do this given how recently the vaccines have been developed. If immunity following vaccination is only relatively short-lived then this increases the level of difficulty in achieving, and critically, maintaining herd immunity. So while we should be most definitely aspiring to achieve herd immunity, we can’t assume this will be achievable and we shouldn’t base all of our decisions on this outcome.

Related: Some Victorians in Sydney allowed to return home as Daniel Andrews rejects tennis players' demands

This won’t be the last time that issues around the vaccines raise questions. We have seen in the last few days concerns following the deaths in older frail individuals in Norway. In dealing with all questions that come up, however, it is important that we are calm, measured and rigorous in our responses. The other inevitability is that many things will change in terms of the evidence we have to draw on and as well as the availability of vaccines, and it is clear that refinements to our vaccination strategy will occur as we deal with this pandemic. However, what we shouldn’t lose sight of is that we have the luxury of options because of both our wealth as a nation as well as the fantastic position we are in terms of crushing virus transmission.

There is no doubt that we also have some unique challenges to grapple with in Australia, including getting the vaccine delivered throughout our vast country, which is a logistical challenge that we cannot underestimate. For now, we should grateful for the position we are in, celebrate that we have guaranteed access to a number vaccines that are safe and effective, and look forward to our vaccination to protect both our own health as well as others across the country.

• Hassan Vally is an epidemiologist and associate professor in public health at La Trobe University