As COVID-normal society reopens, what risk do the unvaccinated pose?

As first-dose vaccination rates pass 87 per cent in NSW and 80 per cent in Victoria, the states are set to reopen with a society segregated along vaccination status.

In Victoria, you’ll need two doses of vaccine to dine or drink inside, go to the office, go to a wedding or a funeral, or to get a haircut.

A man receives a Pfizer vaccine for COVID-19 at Waterloo in Sydney.Credit: Dominic Lorrimer

In NSW, lockdown orders will likely be lifted on October 11, but only for the fully vaccinated. They can have people around to their home, head to swimming pools and gyms, and even go to the zoo.

The unvaccinated will have to wait till December 1 to get their freedoms back. But they now face companies taking their own action. Qantas is making vaccination mandatory for its workers, while anyone who wants to attend a University of Melbourne campus will need a jab.

In Melbourne, as well as healthcare workers and school staff, all construction workers will need to be inoculated, as well as all those authorised to work.

Once we reach 80 per cent vaccination, how much risk does an unvaccinated person pose in terms of spreading the virus?

Unvaccinated people pose a significant risk of spreading the virus as lockdowns ease and the number of COVID-19 cases picks up, experts say.

This is primarily because they are much more likely to catch the virus – and much more likely to pass it on – than people who have been vaccinated.

This is not a major problem when there are few cases. But models project substantial increases in caseload as restrictions are wound back.

“It’s more about how much COVID is around,” says Professor David Tscharke, head of the department of immunology and infectious diseases at the Australian National University.

“The more unvaccinated people there are, the greater the opportunity the virus has to spread. The more virus is around, the more infected people there are in the room. The more virus there is in the room, the more likely you are to be exposed to the virus.”

Long queues for vaccination outside the Exhibition Centre in Melbourne in August.Credit: Getty

Modelling by Professor George Milne’s University of WA team suggests if Australia were to reopen with 80 per cent of people vaccinated, some 80 per cent of cases would be in the unvaccinated.

The goal of segregating the vaccinated and the unvaccinated was to keep overall case numbers low, said Professor Tscharke.

“This is not a measure that is put in place to protect individuals who happen to be vaccinated. It is a policy that is put in place to cut the amount of COVID-19 that is spread in the community as a whole.”

Professor Vlado Perkovic, dean of medicine at the University of NSW, said those who chose to remain unvaccinated would put everyone’s safety at risk.

“It’s like driving without headlights, or perhaps with your eyes closed. It puts the individual’s risk up dramatically, but also increases the risk of all those around them who don’t have a choice in the matter,” he said.

“No one wants to restrict an unvaccinated person’s freedom, but other people have a right to not be exposed to large amounts of virus.”

Do unvaccinated people face any risk from the vaccinated?

“They sure do,” said CSIRO public health expert Dr Rob Grenfell.

People who are vaccinated can catch and spread the virus, although at much, much lower rates than unvaccinated people.

This is primarily because they are much less likely to catch the virus in the first place.

Ambulances at Northern Hospital in Epping. Credit: The Age

Even if they do catch it, they are between 36 and 65 per cent less likely to pass on the virus, new UK data suggests.

In general, catching the virus does not pose a serious risk to a vaccinated person, due to the robust protection they enjoy from the vaccine.

But if a vaccinated person passes the infection on to an unvaccinated person, they are much more likely to become very unwell.

They are 10 times more likely to be hospitalised, and 10 times more likely to die, than vaccinated people.

“We all still need to maintain a degree of caution, especially around the vulnerable groups,” said Dr Grenfell.

What about indirect risks?

People who choose to remain unvaccinated pose a substantial indirect risk to society.

That is primarily because they are more likely to spread the virus. But because they are more likely to end up in hospital, they strain the healthcare system, which can lead to worse care for everyone.

“Unvaccinated people will continue to be admitted to hospital and will continue to strain our health system,” said Dr Grenfell. “I’m going to be pretty cheesed off if the intensive care unit can’t take me if I fall off a ladder or crash my car.”

Globally, unvaccinated people pose a risk because they allow the virus to continue to circulate, increasing the chances of a new vaccine-resistant variant evolving.

The SARS-CoV-2 virus particles which cause COVID-19. Credit: AP

Are there any people who are at particular risk?

Yes. Vaccinated elderly people and those with compromised immune systems are most at risk of so-called “breakthrough infections”, with data suggesting they don’t acquire as much immunity from vaccines as the general population. So people who are not vaccinated pose major threats to those people, whether they have had the jab or not.

About 3 per cent of the adult population have moderately or severely compromised immune systems. A small number of people with specific allergies and underlying health conditions also cannot be vaccinated.

There is also some evidence vaccines are less effective in older people.

AstraZeneca’s effectiveness against infection, for example, falls from 73 per cent for those under 34 to 54 per cent for those over 34 (protection against hospitalisation and death appears to hold up). The average age of a person who has a breakthrough infection is 58. People over 50 generate lower antibody levels than those under 50.

“Remember, one of the most important underlying conditions is age,” said Professor Tscharke.

Of the very small proportion of people who die from a breakthrough infection, most are elderly: the median age in the US is 82. The US has announced a vaccine-booster program for those aged over 65.

Long-term, is everyone going to be exposed to the virus?

The federal government advises that, over time, everyone in Australia will eventually be exposed to COVID-19, immunised or not.

It remains unclear how this will affect our immunity over time, scientists say.

People who have been infected and vaccinated appear to have even stronger immunity against the virus than those who are vaccinated, likely because they have been exposed multiple times.

People who have been infected but have not been vaccinated do enjoy immunity that is similar to or slightly worse than the immunity generated by two doses of AstraZeneca or Pfizer.

It may be that the effect of natural breakthrough infections on people who are already vaccinated over time increases Australia’s overall immunity to very high levels, said University of Sydney vaccine expert Professor Robert Booy.

“Many immunologists are tantalised by this possibility, which might mean the faster evolution of the virus to endemicity. It may be circulating, but as a mild virus.”

Liam Mannix’s Examine newsletter explains and analyses science with a rigorous focus on the evidence. Sign up to get it each week.