Not all masks are created equal, but they’re better than nothing against BA.4 and BA.5

As Australia’s health authorities and governments debate public health mandates in response to a surge in COVID-19 infections, experts are instead pushing for improvements in public information and awareness.

Public officials, premiers and prime ministers no longer front structured press conferences every day, but COVID-19 has continued to evolve into more transmissible variants.

In Australia, health authorities are concerned about the impacts a winter surge might have on the nation’s hospitals, prompting a widening of booster eligibility and a reduction in reinfection periods to 28 days.

Amid their communications has been one consistent point: the new Omicron subvariants BA.4 and BA.5 have greater transmissibility, prompting a return to discussions of viral reproduction rates.

Personal protection against infection is also back on the agenda, with state health officials recommending masks, physical distancing and regular testing, among other measures.

These measures help reduce the spread of the disease. So just how infectious are these new strains? 

There are two ways of measuring the virus’ reproduction rate

In the early days of the pandemic, nightly news reports started discussing COVID-19’s basic reproduction rate – or R0.

This number measures the average number of others that one person with the disease will infect, and was a useful indicator at the onset of the pandemic.

That’s because SARS-CoV-2 – the virus which causes COVID-19 – was brand-new amid a population with no immunity.

It was also free to spread, with governments around the world dithering over what restrictions and lockdowns would look like early on.

When the R0 number is less than 1, the disease will decline and die out. Over 1, and the spread will increase. Early estimates had the original strain’s R0 at 1.5-3.5.

Based on that, every person with COVID-19 would infect around 3.5 others on average.

Those people would then each infect another 3.5, and so on.

But as the virus progressively evolved over the last 2.5 years and increased its transmissibility, the world around COVID-19 has also changed.

At the start of the pandemic, it was suggested one person could infect 3.5 others on average / Credit: Peter Dazeley / Getty Images

And that’s why we should look at effective reproduction rates

While there are new, easily spread COVID variants, there are other factors that can limit transmission.

The most obvious one is immunity.

With vaccination programs and prior infection building resistance to the disease, collective vulnerability to the illness is in far better shape than it was in March 2020.

Restrictions, public safety actions (like wearing facemasks) and other health measures also introduce new factors that influence the chance of passing infection on.

So while a basic reproduction rate could be mind-bogglingly high in theory, reality is often less stark.

It’s why the effective reproduction rate – or Reff – is important in giving a contextualised figure: it measures the average number of people an infected person has actually passed the disease to.

“The Reff number, in Australia at the moment, is over 1, most likely about 1.2, but perhaps as high as 1.4,” says James McCaw, a professor in mathematical biology at Melbourne University.

As McCaw explains, the effective reproduction rate is reflective of the on- ground situation of disease spread.

At play is the protective actions implemented to prevent infection against the virus’ ability to spread in the population.

Just as people can prevent transmission through health measures, the virus can evolve to ignore immunity. One reason new subvariants can reinfect people is because of this “immune escape”.

But this doesn’t mean the virus is inherently more infectious, as a basic reproduction rate is meant to indicate – just that we might be more vulnerable.

“Omicron subvariants spread because they have partially evaded the immunity we have through vaccination and previous infections,” McCaw says.

“While Omicron and its successive subvariants could evolve to be naturally better at infecting a person, there are many factors at play that keep the likelihood of an infection occurring low – that includes vaccination, community and public health actions.

“Just like for influenza, SARS-CoV-2 viruses that mutate to evade our immune system are more able to spread through the population. They don’t need to have a higher intrinsic transmissibility – measured by R0 – to do this.”

“Importantly, the immunity we do have provides longer lasting protection against severe disease, hospitalisation and death than against infection.”

Health messaging needs a booster

The fact vaccines still provide effective protection against new subvariants is a message governments have ramped up since the start of July in anticipation of a surge in cases.

They’ve also issued advice dropping the reinfection period to 28 days, and brought back recommendations to wear facemasks indoors and high-density settings.

While the question of mandated restrictions plays out in the public arena, with the Victorian government choosing on Wednesday to recommend – rather than require – people to mask-up, experts are calling for trusted messengers to provide accurate information to people on the ground.

One such person is Professor Margie Danchin from Murdoch Children’s Research Institute, who observed the community push back against the “big stick” approach taken to government mandates in previous years.

She told The Age that trusted messengers like scientists, medical professionals or informed community leaders can be effective at communicating important public health information.

That could be information regarding the best type of facemask to use, not just the recommendation to wear them.

While research from the University of California found cloth masks lower the odds of testing positive to COVID-19 by 56%, a surgical mask reduces the probability by two-thirds, and a respirator (N95/KN95) by 83%.

A chart showing the effectiveness of infection reduction of three types of mask and no mask. Text reads: people who reported always wearing a mask in indoor public settings were less likely to test positive for covid-19 than people who didn't. Wearing a mask lowered the odds of testing positive among 534 participants of reporting mask type. A respirator is show to have 83% lower odds of infection, a surgical mask is shown to have 66% lower odds, a cloth mas is shown to have 56% lower odds than not wearing a mask.
Credit: Centres for Disease Control and Prevention

But it has been suggested that the priority should be on trying to “nudge” people towards adopting better personal health measures, rather than demanding them.

“We want people to use a mask product. If people do have access and the means to go out and upgrade their product, we certainly want to encourage that,” says Holly Seale, an associate professor from UNSW’s school of population health.

“If you’ve only got a cloth mask, that’s great, let’s use those.”

Not everyone speaks the “language” of COVID-19, and it’s why leaders and professionals need to resume the methods of communication employed amid previous waves.

Recent research led by Seale found barriers to providing useful information to culturally and linguistically diverse communities which experience disparity in illness and mortality from the disease.

And although improvements in communicating to these communities improved over the course of the pandemic, Seale is concerned resourcing to ensure effective COVID-19 communication for everyone may be in decline.

This could be exacerbated by complacency within the population.

“We will certainly see a sense now of ‘we know this, we don’t need to be reading up more’ among people, and that’s a been a challenging thing,” she says.

“If this is going to be something where we are going to sustain a longer surge of infections, we need to think about what worked well back in late 2020 and 2021, really trying to bump those vaccine levels back to the numbers we wanted.

“For communities it’s about word of mouth, and out through all those channels we learnt worked effectively – the local social media feeds or WhatsApp groups.

“That takes a little bit of time, but this is what we need to do right now if we want to reduce the pressure on hospitals by getting people to use masks and get their vaccines up-to-date.”

Please login to favourite this article.