Life as we knew it before the pandemic seems all but a distant memory.

It has been 19 months since Australia recorded its first COVID-19 case on 25 January 2020, and since then, we have endured illness, heartbreak and many lockdowns. Now more than ever, the question on everyone’s mind is, ‘when will this all be over?’.

The short answer is that Australia will return to pre-pandemic life when the population achieves herd immunity. While this may seem like a distant fantasy, a potential path of vaccines and virus suppression may get us there.

Today, we will look to the future and outline how we might get to the promised land of herd immunity.

1. What is herd immunity, and why is it important?
2. How close is Australia to herd immunity?
3. Will we ever get to herd immunity?

What is herd immunity, and why is it important?

Herd immunity (or population immunity) occurs when enough people are immune to a disease such that it stops spreading efficiently and begins to fade away. As a result, even people without immunity are protected by “the herd” as they are significantly less likely to encounter the virus. A population achieves herd immunity through a combination of vaccinations and natural immunity from past infections.

This phenomenon occurs because the immunity of a large group insulates people who are not immune from the disease. An unvaccinated individual will be protected from COVID-19 if every close contact is vaccinated because it will significantly reduce their interactions with the virus. In other words, herd immunity ring-fences people from contagious exposure.

NPR developed some great simulations of how viruses spread in different vaccination settings.

The contagiousness of the disease most notably determines the vaccination threshold necessary for herd immunity. For measles, communities must vaccinate 95% of the population to achieve herd immunity. When a population reaches this threshold, the remaining 5% are protected because vaccinated people shield their interactions with the disease. For polio, the herd immunity vaccination threshold is around 80%. While scientists have not yet identified a specific vaccination rate for COVID-19 herd immunity, approximations range from 60-70% to 85% due to the more contagious Delta variant.

As a new virus, it is difficult to identify the necessary vaccination rate for COVID-19 herd immunity because scientists are still studying its transmission. Furthermore, this vaccination threshold is a complex function of many variables. For example, a higher baseline level of COVID-19 infections, stricter lockdown restrictions, and less contagious COVID-19 variants decrease vaccination requirements for herd immunity. While we cannot identify the magic number of vaccines needed for herd immunity, reaching this goal will see a significant decrease in COVID-19 cases as vaccinated communities protect those without immunity.

Therefore, countries are scrambling to vaccinate their populations in hopes of reaching the promised land of herd immunity.

How close is Australia to herd immunity?

Unfortunately, Australia is still some way off achieving herd immunity. With 17.6% of the population fully vaccinated and low natural immunity levels, Australia lags behind countries like the UK who have fully vaccinated 57.6% of their people (numbers accurate at 7 August 2021).

Additionally, Australia has a low level of natural immunity because the country was very effective at suppressing the virus during and after the first and second waves. Fewer Australians have been infected, hospitalised, or died from COVID-19 than countries closer to herd immunity, such as the UK and the USA. Because COVID-19 infected comparatively fewer Australians, fewer people acquired natural immunity against the virus. Consequently, Australia needs a higher vaccination rate to achieve herd immunity.

Therefore, while the low level of natural immunity against COVID-19 is undoubtedly a good result for Australia, the low vaccination rates leave Australia in a precarious position. Australia must urgently accelerate vaccinations to achieve herd immunity.

Will we ever get to herd immunity?

We hope so.

With a combination of increasing vaccinations and physical distancing restrictions, Australia can quash the spread of COVID-19. However, the virus has made a habit of overstaying its welcome, so we cannot neglect the possibility that COVID-19 is here for the long(er) haul.

The apparent barrier that might prevent us from reaching herd immunity is vaccine hesitancy. The misinformation surrounding vaccines and the global lack of trust in our politicians and the pharmaceutical industry has stoked anti-vaccination sentiments in Australia and overseas, amplified by social media. Indeed we see that vaccination rates in countries such as the USA and the UK are starting to plateau far short of the numbers required for herd immunity. These governments are rightfully concerned that they may not reach herd immunity and are being as proactive as they can to address misinformation and make vaccines available.

Australia is typically more pro-vaccination than these comparator countries, so we hope that Australians can meet the challenge of herd immunity through vaccination. However, we won’t know if we will get there until we reach the higher numbers and our vaccination curve starts to flatten. What may be more of a challenge for Australia is people delaying vaccination to wait for Pfizer or Moderna rather than getting AstraZeneca now. These delays could see us living with COVID-19 far longer as herd immunity is delayed and risk us having to combat a new variant, potentially worse than delta.

Mutations occur more often when transmission rates are high because there are more opportunities for the virus to mutate when rapidly duplicating and spreading. A more contagious COVID-19 variant will increase the necessary vaccination rate for herd immunity, making it more challenging to achieve this end goal. Therefore, even as vaccination rates rise, governments should continue to limit the spread of COVID-19 to prevent the risk of variants mutating.

Another concerning scenario is that mutations may create variants resilient to existing vaccine technologies, making the available vaccines no longer effective. Evidence suggests that our existing vaccines have slightly lower efficacy against the Delta variant; it is conceivable that future variants may pose a more significant threat. Hence, a path towards normalcy requires regularly innovating booster shots and suppressing COVID-19 cases by imposing restrictions where necessary. By limiting the number of COVID-19 cases, Australia reduces the chances of the virus evolving into a more contagious and threatening variant.

With so many ways that COVID-19 could mutate, it may be unrealistic to eradicate COVID-19. Therefore, Australia may have to accept the virus as endemic. COVID-19 may persist in our population at a predictable baseline level, similar to the flu. In such a world where COVID-19 variants continue to evolve, scientists need to regularly develop booster vaccines to reduce the incidence and severity of these strains. However, if countries effectively manage this threat, the world could feasibly return to normal without significant suffering or loss of life. For example, Singapore has outlined a plan for living with an endemic COVID-19 (link). Crucially, for any of these plans to arise, vaccinations and herd immunity are necessary.
While we may never entirely escape the threat of COVID-19, it is reassuring to know there could be light at the end of the tunnel.