Should we vaccinate children against COVID-19? We asked 5 experts


Phoebe Roth, The ConversationAustralia’s Therapeutic Goods Administration (TGA) recently announced provisional approval for the Pfizer vaccine to be used in 12-15-year-olds.

We learned on Monday that the Australian Technical Advisory Group on Immunisation (ATAGI) has advised that Aboriginal and Torres Strait Islander children aged 12-15, those who live in remote communities, and those with underlying medical conditions should be prioritised to receive the jab.

With COVID vaccination for kids being such a hot topic, we asked five experts whether we should vaccinate children in Australia against COVID-19.

Four out of five experts said yes

Here are their detailed responses:

If you have a “yes or no” health question you’d like posed to Five Experts, email your suggestion to:


Asha Bowen is co-chair of the Australian and New Zealand Paediatric Infectious Diseases (ANZPID) group of the Australasian Society of Infectious Diseases. She receives research funding from NHMRC.

Catherine Bennett has received NHMRC and MRFF funding, and is an independent expert on the AstraZeneca advisory board.

Julian Savulescu receives funding from the Wellcome Trust. This work was supported by the UKRI/AHRC funded UK Ethics Accelerator project, grant number AH/V013947/1.

Margie Danchin is a member of ATAGI’s working group on vaccine safety, evaluation, monitoring and confidence.

Nicholas Wood holds an NHMRC Career Development Fellowship and Churchill Fellowship.The Conversation

Phoebe Roth, Deputy Editor, Health+Medicine, The Conversation

This article is republished from The Conversation under a Creative Commons license. Read the original article.

If I’ve already had COVID, do I need a vaccine? And how does the immune system respond? An expert explains

Andre Coelho/EPA/AAP

Sunit K. Singh, Banaras Hindu UniversityOver a year into the pandemic, questions around immune responses after COVID continue to confound.

One question many people are asking is whether the immunity you get from contracting COVID and recovering is enough to protect you in the future.

The answer is no, it’s not.

Here’s why.

Remind me, how does our immune response work?

Immune responses are innate or acquired. Innate, or short-term immunity, occurs when immune cells that are the body’s first line of defence are activated against a pathogen like a virus or bacteria.

If the pathogen is able to cross the first line of defence, T-cells and B-cells are triggered into action. B-cells fight through secreted proteins called antibodies, specific to each pathogen. T-cells can be categorised into helper T-cells and killer T-cells. Helper T-cells “help” B-cells in making antibodies. Killer T-cells directly kill infected cells.

Once the battle is over, B-cells and T-cells develop “memory” and can recognise the invading pathogen next time. This is known as acquired or adaptive immunity, which triggers long-term protection.

What happens when you get reinfected? Memory B-cells don’t just produce identical antibodies, they also produce antibody variants. These diverse set of antibodies form an elaborate security ring to fight SARS-CoV-2 variants.

Natural immunity is not enough

Getting COVID and recovering (known as “natural infection”) doesn’t appear to generate protection as robust as that generated after vaccination.

And the immune response generated post-infection and vaccination, known as hybrid immunity, is more potent than either natural infection or vaccination alone.

People who have had COVID and recovered and then been vaccinated against COVID have more diverse and high-quality memory B-cell responses than people who’ve just been vaccinated.

Studies indicate mRNA vaccines generate a more potent immune response with previous infection, at least against some variants including Alpha and Beta.

And studies have shown that antibody levels were higher among those who’d recovered from COVID and were subsequently vaccinated than those who’d only had the infection.

Memory B-cells against the coronavirus have been reported to be five to ten times higher in people vaccinated post-infection than natural infection or vaccination alone.

Is one dose enough after COVID?

Some reports have suggested people who’ve had COVID need only one dose of the vaccine. Clinical trials of approved vaccines didn’t generate relevant data because people who’d already had COVID were excluded from phase 3 trials.

One study from June showed people with previous exposure to SARS-CoV-2 tended to mount powerful immune responses to a single mRNA shot. They didn’t gain much benefit from a second jab.

A single dose of an mRNA vaccine after infection achieves similar levels of antibodies against the spike protein’s receptor binding domain (which allows the virus to attach to our cells) compared to double doses of vaccination in people never exposed to SARS-CoV-2.

We need more studies to fully understand how long memory B-cell and T-cell responses will last in both groups.

Also, a single dose strategy has only been studied for mRNA-based vaccines. More data is required to understand whether one jab post-infection would be effective for all the vaccines.

At this stage, it’s still good to have both doses of a COVID vaccine after recovering from COVID.

Does Delta change things?

The development of new vaccines must keep pace with the evolution of the coronavirus.

At least one variant seems to have evolved enough to overtake others, Delta, which is about 60% more transmissible than the Alpha variant. Delta is moderately resistant to vaccines, meaning it can reduce how well the vaccines work, particularly in people who’ve only had one dose.

There’s no data available yet about how effective a single jab is for people who were previously infected with Delta and recovered.

Read more:
Why is Delta such a worry? It’s more infectious, probably causes more severe disease, and challenges our vaccines

The most important thing you can do to protect yourself from Delta is to get fully vaccinated.

According to a Public Health England report, one dose of Pfizer offered only about 33% protection against symptomatic disease with Delta, but two doses was 88% effective. Two doses was also 96% effective against hospitalisation from Delta. The AstraZeneca vaccine was 92% effective against hospitalisation from Delta after two doses.

A few vaccine manufacturers, including Pfizer, are now planning to use a potential third dose as a booster to combat the Delta variant.The Conversation

Sunit K. Singh, Professor of Molecular Immunology and Virology, Institute of Medical Sciences, Banaras Hindu University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Vaccine selfies may seem trivial, but they show people doing their civic duty — and probably encourage others too



Louise Grimmer, University of Tasmania; Gary Mortimer, Queensland University of Technology, and Martin Grimmer, University of Tasmania

Have you been vaccinated yet? And if you have, are you one of a growing number of people who posted a selfie on social media afterwards? At a time when many people distrust government advertising, vaccine selfies — or “vaxxies” — may well be the secret weapon to encourage more people to get the jab.

Suddenly our Facebook, Twitter and Instagram feeds are filling up with selfies of family, friends and even strangers getting their COVID shot.

But vaxxies are more than mere selfies, as they have a unique social function. They are likely helping normalise the vaccine procedure, reducing hesitancy around perceived risks and increasing vaccine trust within social circles.




As governments and health officials continue to flip-flop on vaccine age requirements, and anti-vaxxers spread falsehoods through social media and protests, the vaxxie might just be a powerful line of defence against vaccine hesitancy.

Read more: Public protest or selfish ratbaggery? Why free speech doesn’t give you the right to endanger other people’s health

As of July 21, more than 10.6 million COVID vaccine doses had been administered in Australia. As time passes, more and more people are showing their support by posting about their vaccination experience online.

Normally, we see this type of behaviour demonstrating “civic duty” during elections or with social movements such as Pride or Black Lives Matter. We’re now seeing similar posts involving vaccination, using a variety of hashtags including #vaxxie, #GetVaccinated, #GetVaccinatedNow, #Vaccination and #jab.


In friends we trust

The vaxxie could be a useful tool in encouraging people to get vaccinated. Over the past decade in particular, there has been an erosion of trust in traditional advertising and a huge surge in social media use.

This means word-of-mouth recommendations and reviews from people we know (and even people we don’t) are often considered more “authentic” than standard advertising and government messaging.

Read more: Australia’s new vaccination campaign is another wasted opportunity

Research indicates we look to our friends, family and social groups for guidance during uncertain times. They provide us with subjective norms: the desire to behave as those who are significant to us think we should.

This results in social pressure to engage in certain behaviours. If our family and friends are posting vaxxies, it’s an implicit nudge for us to get vaccinated too. And as reported vaccine shortages continue and demand grows, seeing vaxxies can also increase our fear of missing out (FOMO).


In-groups and out-groups

In the same way one shows support for social movements on social media, sharing a vaxxie communicates your position on vaccinations — you are either pro-vax or anti-vax. Essentially, you are either with us or against us: a hallmark of classic in-group/out-group behaviour.

The psychology of the in-group/out-group is best illustrated using social identity theory. This theory states internal cohesion and loyalty to the in-group exists when the group members maintain a state of almost hostility or assertive opposition toward out-groups — which are often perceived as inferior.

This theory explains spectator behaviour at sporting events. As we see more of our friends sharing their vaxxies, we may desire to be a member of the “in-group”. But to be in this group, we need to get a jab (and show evidence with our own vaxxie).

The in-group pressure may be further increased when we see our political leaders or favourite celebrities get involved. US President Joe Biden, Dolly Parton and Sir Ian McKellen are just some of the icons whose vaccinations made headlines.

Dolly Parton posted her own vaxxie.

Risks of virtue signalling

One of the main risks in posting a vaxxie is it could alienate others through virtue signalling, which is when a person behaves in a way that highlights their own “good” moral values. People on Facebook will often loudly proclaim their support for a certain cause because they want to seem caring or “woke”.

But most of us aren’t impressed by those who overtly express their own moral correctness. There’s a fine line between encouraging others to engage in a certain behaviour and coming across as self-righteous.

There may also be an element of mob mentality at play with vaxxies. Due to excessive pressure from peers, some may find themselves getting vaccinated for emotional (versus rational) reasons. While the pressure to get vaccinated is arguably positive, some individuals may have legitimate concerns which they will suppress in order to conform.

That said, this is not the same as crowd behaviour which is often shrouded in anonymity and involves blindly following others. Vaxxies are personal, identifiable messages and are not anti-social.

Another risk with vaxxies is they may encourage “brand” competition. Vaxxie posters regularly include the hashtag of their vaccine: #pfizer or #astrazeneca.

Given the mixed messaging around AstraZeneca, could a proliferation of Pfizer vaxxies discourage people from seeking out AstraZeneca, at a time when we’re encouraged to take whichever option we can?


Despite the risks, however, it’s clear we will need a variety of tools to encourage people to get vaccinated during this crucial phase of the pandemic. Vaxxies likely have an important role to play on this front.

And as long as they don’t seek to overtly shame or alienate others, they could help engender a strong sense of solidarity as more and more people get the jab.

Read more: ‘Virtue signalling’, a slur meant to imply moral grandstanding that might not be all bad The Conversation

Louise Grimmer, Senior Lecturer in Marketing, University of Tasmania; Gary Mortimer, Professor of Marketing and Consumer Behaviour, Queensland University of Technology, and Martin Grimmer, Professor of Marketing, University of Tasmania

This article is republished from The Conversation under a Creative Commons license. Read the original article.

We’ve heard of R numbers and moving averages. But what are k numbers? And how do they explain COVID superspreading?

Forest Simon/Unsplash

Adrian Esterman, University of South AustraliaFirst thing in the morning, or come 11 o’clock, countless Australians anxiously wait for the daily COVID-19 case numbers, trying to understand whether their outbreak is under control, and how much longer they will be in lockdown.

As well as daily case numbers, people want to know what proportion of cases were infectious in the community, and whether there were any unlinked or “mystery” cases.

People have also been following the daily Reff, or effective reproduction number, hoping it will get below 1, showing public health measures are working to halt the spread.

However, to have a good understanding of the dynamics of an outbreak, it is also necessary to understand k, which shows how much variability there is in daily case numbers.

COVID-19 superspreaders

Many superspreading events have occurred in the current pandemic. An infectious volunteer dressed as Santa Claus, for example, visited a care home in Antwerp in December 2020, and infected 40 staff members and more than 100 residents.

Even more drastic is a South Korean woman who caused a superspreading event resulting in more than 5,000 cases in the South Korean city of Daegu.

Read more:
How to prevent COVID-19 ‘superspreader’ events indoors this winter

Meanwhile in Australia, we have seen many examples of cases being detected, but not infecting a single other person.

So, how can this disparity be explained?

Remind me, what’s the Reff?

The effective reproduction number Reff, also called Re or R(t), tells us, on average, how many people an infected person will pass it on to. Unlike the basic reproduction number, R0, Reff takes into account that some people will be vaccinated or immune, and social distancing is in place.

So, if a virus has a Reff of 2, each infected person (primary case) will on average infect two others (secondary cases).

However, this average hides a huge amount of variability. Most infected people simply infect no one, whereas others (the superspreaders) infect many people.

Read more:
A few superspreaders transmit the majority of coronavirus cases

We’re unsure why this is the case. It could be some people are naturally social animals, or fail to maintain social distancing, mask-wearing, or hygiene.

Alternatively, it could simply be that some people have a much higher viral load than others or tend to emit virus particles as aerosol clouds more than others.

Daily case numbers can vary substantially

During periods of outbreaks, health authorities report daily case numbers. Here they are for Victoria when the fifth lockdown began:

Average daily count

The average (mean) daily count over these ten days is 10.7 cases per day (you can calculate it yourself by adding up all the cases and dividing by ten).

However, there is a lot of variability, with numbers going up and down like a yo-yo from zero to twenty. Because of this variability, we often use moving averages to try and smooth things out.

7 day moving average

For a seven-day moving average, we add up the cases from July 12 to the 18 and divide by 7, to get 8.4. Then we do the same for July 13 to the 19 to get 10.3.

This way, we end up with a much smoother series of numbers without all the up and down jags, that allows us to see trends much more easily. Importantly, I also use the moving average to calculate the Reff.


We measure the amount of variability in the daily case numbers by a statistic called the variance. This measures how far apart the daily counts are from their average value of 10.7. For most count data (for example, the number of days each month you exercise), the average and variance are the same. So, if the average count is 10.7, the variance is 10.7.

However, for this epidemic, because of the superspreaders, the variance is much greater – we call this overdispersion.

So what is the k?

An estimate of how much extra variability or overdispersion there is, is measured by a statistic called k. A small k means the variability is higher than the average daily count, whereas a large k means the variability is closer to the average daily count.

So, with a high value of k (say 2), and a Reff of 2, most infected people would typically infect two others, but it could of course be higher or lower than this.

Source: The Conversation/Adam Kleczkowski (CC-BY-ND)

In the above diagram, the number of people a case infects is shown in each circle. The original maroon (primary) case infects two others (red). Each of these secondary cases infects three or four others (pink), and so the outbreak continues. Typically, most infected people, infect at least one other person.

However, with k close to 0 and a Reff of 2, most people would infect no one else, and there would be one or more superspreaders.

Source: The Conversation/Adam Kleczkowski (CC-BY-ND)

In the above diagram, the primary case (maroon) is a superspreader, infecting 16 other people. Although most of these secondary cases do not infect anyone else, one of the tertiary cases is also a superspreader, infecting 11 others.

In both diagrams the Reff was 2. So, you can see that knowing the Reff is only part of the story.

Estimates of COVID-19’s k range from 0.1 to 0.5. These are very small values, and indicate 80% of secondary infections are caused by around 10% of primary cases. This means the majority of infectious people do not infect anyone.

Read more:
Is the K number the new R number? What you need to know

Why is it useful to know the k?

When an infected person is diagnosed, contact tracers immediately try and find their close contacts. These are then tested and put into isolation. This is called forward contact tracing.

However, in the context of superspreaders, it’s equally important to find out who infected the original diagnosed case, as that person could potentially be a superspreader.

Forward contact tracing of that potential superspreader would likely lead to many more cases being detected. In fact, modelling has found looking backwards as well as forwards could prevent two or three times as many infections. This is known as backward contact tracing and is now widely used in Australia.

The k number shows us the importance of backwards as well as forwards contact tracing.The Conversation

Adrian Esterman, Professor of Biostatistics and Epidemiology, University of South Australia

This article is republished from The Conversation under a Creative Commons license. Read the original article.