The relative losers of the ATAGI announcement, thus far, are the 50 to 69-year-old demographic - the very age group, and elderly Australians, that votes proportionally more for the Coalition. This age group would apparently get AstraZeneca; a vaccine with an efficacy (reduced probability of a vaccinated person getting COVID-19 symptoms compared to having no vaccination) that is lower. Yet younger Australians, who are much less likely to suffer severe symptoms, would get the higher-efficacy Pfizer vaccine, and thus a lower probability of getting symptoms than older Australians.

Differences in efficacy across vaccines really matter. Pfizer provides about 95 per cent efficacy against standard variants of the virus, appears to reduce infectiousness by 90 per cent, has no identified serious side effects with adolescents, and has performed well in actual use in Israel in a study of 1.2 million people. By comparison, the efficacy of AstraZeneca is between 68 per cent and 82 per cent for standard variants.

The third vaccine secured by the Australian government is Novavax, which will be sourced from Europe - but Australia also has the capacity to eventually produce this vaccine. Novavax is expected to start to be delivered in Australia before the end of 2021. Like Pfizer, it also has high efficacy in trials (89 per cent), including with the UK variant, but performs less well against the South African variant (60 per cent efficacy). Enough doses of Novavax have apparently been secured to vaccinate every Australian.

The manufacturers of AstraZeneca, Pfizer and Novavax all claim that their vaccines provide 100 per cent efficacy against getting severe symptoms that require hospitalisation. However, the claim of 100 per cent efficacy against severe symptoms is not supported in the analysis of the data of the published phase 2/3 clinical trials for AstraZeneca, and has yet to be confirmed for any of Australia's three selected vaccines, including Pfizer, in relation to recently identified variants of the virus that cause more severe symptoms.

Fortunately for Australians, on Friday the Prime Minister announced that Australia had, in the fewer than 24 hours following the ATAGI announcement, suddenly secured an additional 20 million doses (40 million in total) of Pfizer. These Pfizer doses, it is claimed, will be available before the end of 2021. It apparently means that almost all adult Australians who wish to be vaccinated with the Pfizer vaccine should, eventually, get it.

The pandemic-stopping question is: why did it take until last Friday, April 9, for the Australian government to ensure that all Australians have access to what is the most preferred of the available vaccines? The poorer efficacy of AstraZeneca has been known for months. New Zealand made the decision to switch exclusively to Pfizer on March 8 because of its higher efficacy. South Africa stopped using AstraZeneca on February 8, because preliminary data indicates that AstraZeneca has low efficacy (possibly as low as 22 per cent) against the South African variant (B.1.351).

So long as Australia's international border controls maintain an effective 14-day supervised quarantine program (New Zealand being the exception), until everyone who is eligible and wishes to has had the Pfizer or Novavax vaccine, the risks of a large outbreak remain low. Quarantine, testing and contact tracing, and physical distancing (including the use of masks) when an outbreak occurs have kept Australians safe. Public safety against COVID-19 also increases when all front-line medical staff and every worker who has contact with persons in quarantine are vaccinated with Pfizer.

A challenge going forward is that there are key misunderstandings about, firstly, why Australia has been so successful in eliminating community transmission, and secondly, the purpose of mass vaccination to prevent the spread of COVID-19. As we learnt in the early months of the pandemic, a lack of information quickly becomes misinformation that can be deadly and is associated with vaccine hesitancy. Thus, we must avoid the miscommunication that has already contributed to the unravelling of Australia's vaccination rollout and a failure to deliver as promised.

Without a rapid course correction, Australia's rollout and a premature opening of its international border could easily result in a third wave of COVID-19 infection, which would have both bad public health and economic outcomes. Before the international border is fully opened, all Australians must have had the opportunity to be vaccinated with a high-efficacy vaccine, such as Pfizer or Novavax.

Vaccination is not just an issue for the elderly and most at risk of severe symptoms or death. COVID-19 can result in long-term health problems (beyond four weeks), including for the young and middle-aged, that reduce quality of life and possibly life expectancy. This may affect up to 30 per cent of those who get symptoms, while 10 per cent can have symptoms lasting longer than 12 weeks.

What has kept Australia (and New Zealand) safe from COVID-19 so far has been strict protocols on all arrivals from overseas, including testing of all arrivals and 14-day supervised quarantine. Without these protocols, there is no doubt Australia would have had persistent and frequent reinfections from overseas arrivals that could easily have resulted in a full-blown COVID-19 epidemic.

Since late 2020, several variants of the virus have been identified that appear to be more infectious and cause more severe COVID-19 symptoms. Some of these variants include: the UK (or Kent) variant (B.1.1.7); the South African variant (B.1.351); and the Brazilian variant (P.1). The UK variant has been identified as a key cause of rapidly rising infections and hospitalisation in Europe, Canada and many other countries. As noted by Germany's Chancellor Angela Merkel, Europe's third wave is causing symptoms in a greater proportion of those who are not elderly, such that "now it's middle-aged and also younger patients who must be ventilated". Having a vaccine that has high efficacy against these variants, and is available to everyone in the world, is critical to stopping the pandemic.

Another misunderstanding in relation to the Australian vaccination rollout is herd immunity. Provided that vaccines prevent infections, in addition to preventing symptoms, and if a sufficient proportion of the population is vaccinated, the unvaccinated are also protected from contracting the disease. This is because the "chain of infection" is stopped, and while disease outbreaks may still occur, they do not lead to an epidemic.

The proportion of the population that needs to be vaccinated to get herd immunity varies depending on the infectiousness of the disease and the ability of the vaccine to reduce the infectiousness of those who contract the disease. The virus that causes COVID-19 is highly infectious. Thus, to reach a herd immunity threshold from the newer and more infectious variants will, based on our calculations, require at least 80 per cent of the Australian population to be vaccinated - assuming all susceptible people receive the Pfizer vaccine, that it reduces infectiousness by 90 per cent and that each infected person, on average, infects 3.5 people in the absence of social distancing or vaccination. Reaching this threshold is a challenge, but it is possible because in a February survey over 64 per cent of Australians said they would definitely get vaccinated, 27 per cent were undecided and 9 per cent stated they would definitely not get vaccinated.

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In our view, herd immunity is impossible under the original vaccination rollout plan, whereby most Australians would receive the AstraZeneca vaccine. This is because of AstraZeneca's lower efficacy. Lower efficacy likely means lower capability to reduce infectiousness compared to vaccines with higher efficacy, such Pfizer or Novavax. Importantly, overcoming vaccine hesitancy is critical to achieving herd immunity. Fewer people will now accept the AstraZeneca vaccine because of the risk, albeit very low, of blood clots.

Meanwhile countries, like the United Kingdom and the United States that performed so badly in suppressing COVID-19 may possibly achieve herd immunity this year, well ahead of Australia, because of their highly effective vaccination programs and because a much higher proportion of their populations have already been infected.

At some point Australia's 14-day quarantine will end, but it should not happen before Australia has made its best effort to achieve herd immunity. Given the potential for new variants to cause further outbreaks, and the likelihood that antibodies for COVID-19 will decline over time, Australians will also need to be revaccinated periodically. Even with vaccinations for all Australians it would still be sensible to maintain, indefinitely, low-cost border controls such as: rapid testing of all overseas arrivals so that only those with a negative test can leave the airport or port; proof of vaccination for all international travellers (with exceptions for infants and young children); and all passengers (with appropriate exceptions) being required to wear masks on aircraft and in airports.

Whichever way you look at it, from the social, economic or the public health angles, this is a "no brainer". The Australian government must ensure that all Australians get vaccinated as soon possible, with vaccines that are the least affected by jab-hesitancy and have the highest possible efficacy. This is the only acceptable way to achieve herd immunity.

Then, and only then, should Australia's supervised quarantine for all international arrivals (with the exception of New Zealand) be relaxed. To do otherwise is to snatch defeat from the jaws of victory, and would place millions of Australians at risk of contracting COVID-19.