Inside the shifting vaccine strategy
As the government declares an end to the latest wave of infections, it has also quietly moved away from vaccine targets and is depending on hybrid immunity.
Quietly, and without much fanfare, Australia’s chief medical officer declared an end to the nation’s latest and most protracted Covid-19 outbreak last week. In doing so, he signalled a decisive shift away from crisis mode on the millennium’s most infamous disease.
While community transmission of SARS-COV-2 continues apace, and is likely to remain at high levels for at least the next two years, Professor Paul Kelly said Australia had reached a significant milestone in the first few months of 2023: almost every citizen is now immune.
Hybrid immunity, which refers to the combination, at a population level, of antibodies from either past infection or vaccination against Covid-19, has now reached 99.6 per cent, according to the latest estimates from the Department of Health.
This won’t be permanent, of course. Individual immunity declines over time, most markedly after six months for vaccination and over a perhaps slightly longer window after a primary infection, but we are amid the paradigm shift from pandemic to endemic.
Absolute vaccine targets have been shelved. The focus is now on time since last booster, and the advice for most healthy adults is that while booster vaccines will remain freely available, the benefits may be marginal, and it’s a matter of personal choice.
The Australian Technical Advisory Group on Immunisation (ATAGI) recently updated its official position on the Covid-19 booster program to move away from blanket recommendations in favour of a strategy targeting the highest-risk groups: older Australians and people with a disability or complex medical comorbidities.
“This is primarily because younger, healthy people and most children don’t really get severe disease, especially now that most have had infection and/or previous vaccination, and now that we have the Omicron strain,” Professor Allen Cheng, an ATAGI member, told The Saturday Paper.
The fourth Omicron wave, which lasted 19 weeks and officially hit its nadir in late February, was hailed by Kelly as evidence
that, while a “variant soup” of SARS-COV-2 continued to circulate, Australia had broken the back of the Covid-19 pandemic.
Despite there being “virtually no public health and social measures in force in the general community” over this period, Kelly said, hospitalisations and intensive care admissions were much lower compared with previous Omicron outbreaks and there had been “substantially fewer overall deaths”.
In his communiqué, Kelly wrote:
“This is testament to the very high levels of vaccination coverage, hybrid immunity and ready access to oral antiviral treatments.”
Health officials are no longer sweating over case numbers and surveillance has shifted to more traditional infectious disease methods: emergency room and ICU data, mortality rates. In an era of antibody saturation, and where there are effective antiviral treatments, the health system cares less about how many people are getting sick and more about how sick they get.
Navigating this message at a population level is fraught, however. At-risk populations need to be engaged, while others need to be reassured that boosters are not necessary for everyone.
“The messaging is a dog’s breakfast, but one that we almost can’t avoid,” says Professor Julie Leask, an expert in immunisation.
“Three years into a pandemic it’s always going to be like this – complex, changing, constantly oscillating, until you start to settle into something that is a little more predictable.”
Part of the problem is structural, according to Leask.
ATAGI is an inherently technical body, which is tasked with assessing and synthesising the latest evidence regarding vaccines and advising the federal government. While it attempts to consider implementation issues in the course of its deliberations, this isn’t done in a systematic, formalised way, falling outside its remit and beyond the scope of its membership.
Vaccine rollout was once the domain of the National Immunisation Committee, a representative group bringing together various stakeholders including primary care nurses, specialist medical colleges, the Australian Medical Association, the National Aboriginal Community Controlled Health Organisation and jurisdictional controllers to discuss implementation logistics.
This body, which deliberated separately from, and provided formal advice to, ATAGI on issues including promotion and messaging, was mothballed by the Morrison government in 2019, prior to the pandemic.
Without this intermediary between the science and its application at population level, Leask says, the official advice was overly detailed and complex, with more caveats than clarity.
“The more nuanced and evidenceinformed and precise your vaccination recommendations are, the less easy it is to communicate and implement, and that’s a tension we have,” Leask says. “You end up trading adherence to evidence in the advice against implementability of it.”
Vaccination research supports the government’s national messaging push. Broad-based recommendations are more likely to reach the people who need to hear them. If a GP is able to, by fiat of simple and straightforward eligibility advice, give most people in front of them the same consistent message, they are more likely to capture a greater number of patients overall, including people in the high-risk group.
As it stands, already beleaguered primary-care providers are having to wade through the criteria and counsel each patient accordingly, an unwieldly and timeconsuming task that feeds into hesitancy, particularly in pockets where uptake has been cruelled by misinformation and mistrust.
This issue is particularly pronounced in disadvantaged communities. Dr Mariam Tokhi, a Melbourne GP working with refugees and asylum seekers, says people have stopped asking for the Covid vaccine. Even when she offers it in conjunction with the newly available seasonal flu booster, they refuse.
“I can tell you that my patients certainly don’t know what the recommendations are,” Tokhi says. “I’m not sure they are reaching the populations I see.”
Leask, who sits on the World Health Organization’s South-east Asia regional advisory group for immunisation programs, related a similar story from a recent workshop with a migrant community in Western
Sydney, where she said some participants did not know there were recommendations for anything beyond two doses.
“Your postcode does determine whether you are more likely to have a booster or not,” says Leask, noting “very significant poverty gradients with respect to booster uptake” and continued inequities of access not only to vaccines but also the latest advice.
This was why, even though it risks muddying the message and confusing or losing the broader population, Leask says specifically mentioning at-risk groups in media messaging – people with “disability, with significant or complex health needs” – was a necessary “matter of equity”.
“Those groups need to hear: ‘I see you, the system sees you and acknowledges your needs,’ ” she says. “Maintaining trust is through action, but it’s also in rhetoric.”
Much of what we do next will be informed by what we already know about Covid-19.
It is incredibly infectious, more dangerous the older you get, and can evade, in current evolutionary form, a degree of immunity conferred by vaccines.
According to seroprevalence surveys of Australian blood donations, at least seven in every 10 people have had Covid-19 in the past six months – and that number is likely much higher given that the latest data was gathered before the Christmas surge.
This is especially true for 18- to 39-yearolds, among whom cases continue to be concentrated – likely because of their mobility and mixing. It is also the group in whom there is a small but well-demonstrated risk of serious adverse effects from MRNA vaccines.
For every one million Pfizer or Moderna doses delivered among this age group, about 40 recipients will develop myopericarditis, an inflammation of the heart muscle and its lining that can have serious lasting effects.
In the setting where many if not most people in this age group are likely to be immune from prior infection or earlier vaccines, the small benefit of a booster may or may not outweigh this small but real risk.
The National Centre for Immunisation Research and Surveillance recently held a webinar for vaccine providers on the 2023 booster program and ATAGI advice. Dr Ben Smith, a paediatrician by training and staff specialist at the centre, told the forum that a booster for a healthy young person would at most reduce their risk of mild or symptomatic disease by 30 to 40 per cent.
While boosters offered “significant additional protection against severe disease” for high-risk populations, especially people older than 65, they were unlikely to make much of a difference right now in terms of absolute risk of severe illness for many, Smith said.
Numbers from the British ATAGI equivalent, the Joint Committee on Vaccination and Immunisation, provide some useful context.
According to its analysis, which is closely watched by ATAGI, for people aged in their 40s it takes 80,000 fourth-dose boosters to prevent a single hospitalisation. For people aged in their 50s, it takes 8000 boosters to prevent one hospitalisation. For people aged over 70, it takes just 800.
Advancing age is the single greatest risk factor for poor outcomes from Covid-19. A healthy 80-year-old is 30 times more likely to die than someone aged 50. Compare this with cancer – the highest-risk comorbidity for SARS-COV-2 infection – which only carries a threefold increased risk of death.
Professor Kelly laid this out in stark terms in his latest missive, detailing the particular inroads made in Australia to improve Covid-19 outcomes in aged care.
Early in the pandemic, Kelly said, one aged-care resident in every three who was infected with Covid-19 died from it. That number is now closer to one in 40. The case fatality rate in this population was 5.6 per cent during the first Omicron wave, but has more than halved to 2.6 per cent.
In large part, this reflects robust vaccine penetrance, with more than 80 per cent of aged-care residents nationally having received at least four doses, as well as very strong uptake of antiviral medications. Of the 70,000 prescriptions issued during the most recent fourth wave, 56,000 were in aged-care facilities.
Some experts have been pushing for antivirals to be made more widely available but Cheng said the substantial reduction in hospitalisation risk demonstrated by the original trials was less clear in an era of hybrid immunity, where the disease profile had evolved.
Procurement of Covid vaccines and treatments was scrutinised last year in an independent review by Professor Jane Halton, commissioned by the incoming Labor government. Her report noted that the supply of “consumables” – antiviral and related treatments – was more than adequate for the next 12 months.
On the question of vaccines, Halton noted that wastage was to be expected in an oversupply environment, and eligibility and priority use recommendations were likely to have an impact.
There are some 12 million bivalent vaccines in the national medical stockpile and, with more than one million boosters already delivered to patients this year, this is likely to be in significant excess to requirements. While declining to comment on vaccine spoilage in dollar terms, a spokesman for the Department of Health said it was expected to remain “within the Who-accepted range of between 15-40 per cent of vaccines”.
There is an ethical element to this waste. Inequities persist globally, with some lower-income nations only recently securing primary course vaccines and struggling to distribute them amid waves of infection.
Leask recently returned from an international summit on immunisation in Seoul, where she reported Covid-19 had been superseded by other concerns for many countries.
“Covid is part of it but most people have moved on to routine immunisation recovery and new threats, measles, flu,” Leask says.
Across the Tasman, New Zealand is grappling with an outbreak of pertussis, the bacteria responsible for whooping cough, with three infants dying in the past six weeks and fears that 11 confirmed cases are just the tip of undetected community spread.
Uptake of routine childhood vaccinations declined globally during the pandemic, including in Australia, particularly for Aboriginal and Torres Strait Islander children. A similar trend has been observed among Aotearoa’s Māori communities, underscoring the same socioeconomic gradient observed in Covid-19 vaccination and disease.
There can be no room for complacency as new variants emerge, potentially affecting transmission, the effectiveness of treatments and the efficacy of vaccines, according to Professor Cheng, who was Victoria’s deputy chief health officer during the pandemic’s peak.
“There are lots of unknowns.”