ALTHOUGH there’s a lot we don’t yet know about the Omicron strain of COVID-19, there is increasing evidence of its ability to evade immunity provided by previous infection.

According to Australian experts, it’s a clear message to people who have already been infected by previous strains that they still need to be vaccinated against COVID-19.

A research letter published in the MJA further backs this up. It describes a case of three household contacts in Melbourne who had separate strains of COVID-19, almost a year apart.

In July 2020, the three adults were diagnosed with the pangolin lineage D.2 (not a variant of concern) during Victoria’s second wave. Two out of the three had mild symptoms, and the third person experienced no symptoms.

In July 2021, the three household contacts were again diagnosed with COVID-19, but this time with the Delta strain (pangolin lineage B.1.617.2).

“The phylogenetic data, together with the link with a known COVID-19 outbreak, indicate that the 2021 COVID-19 diagnoses reflected new infections rather than prolonged viral shedding,” the authors wrote.

This time, all three experienced mild symptoms. They had no known immunocompromising conditions and were not eligible for COVID-19 vaccination at either time.

Before the emergence of the Omicron variant, second infections were thought to affect fewer than 1% of people with resolved COVID-19.

According to one of the MJA study’s authors, epidemiologist Mohana Baptista, what makes this research unique is that they could show reinfection within the same household group almost a year apart.

“The fact that it showed that you can get infected with a different lineage of the virus, I think that is what’s powerful in this letter,” she explained.

The current Australian advice for people who have had COVID-19 is that there is no need to delay vaccination as long as they have recovered from the acute illness. However, they can defer vaccination for up to 6 months as past infection reduces the chance of reinfection for at least this amount of time.

Associate Professor Holly Seale, an infectious diseases social scientist from UNSW Sydney, highlighted that now is the time to get the vaccination message out there for the many people who were infected in the last wave.

“For people who had COVID-19 during the heightened periods of local transmission in New South Wales and Victoria, those people will be coming up to that 6-month mark early in 2022. Having some dedicated resources that go out to them would be really useful,” she said.

She said it’s particularly important in culturally and linguistically diverse communities.

“I’ve been doing a lot of work this year with supporting culturally and linguistically diverse communities and I don’t think I’ve come across any really great resources [where I’ve thought] ‘I like that message’,” she said.

According to Ms Baptista, vaccine teams in Victoria are working on various communication strategies.

“There’s a lot of community engagement underway to look at areas where vaccination rates are low and to try and encourage vaccination,” she said.

There are many reasons why some people haven’t been vaccinated. Some are waiting for some other brand of vaccine, others continue to be fearful of the safety and the way the vaccines were developed.

According to Associate Professor Seale, there’s another group that may need some support.

“There are those people who have self-assessed themselves as being at risk from either a localised or serious adverse event from a vaccine, or have had a previous allergy to a vaccine, and have ruled themselves out of getting the COVID-19 vaccine. What can we do for these adult populations that could support them to get this vaccine?” she asked.

In paediatric settings, there are clinics that provide a specialty service for children who have had an adverse event or have complex health needs.

According to Associate Professor Seale, adults should know there are specialty immunisation services that immunisation providers can consult to make sure they receive the right advice for their patient’s situation.

“Say they’ve had an adverse event, following a flu vaccine, and they’ve just written off getting a COVID-19 vaccine because of that experience. Can these clinics offer an opportunity for a clinical assessment of whether it’s feasible to get vaccinated? Can these clinics then support adults to get vaccinated?” she asked.

Although we don’t yet know the answers to the transmissibility and the severity of the Omicron variant, Ms Baptista said it has highlighted that people can get reinfected.

“There’s the feeling [out there] that if I’ve had COVID-19, I don’t need to get vaccinated. With Omicron and the news of that coming through now, particularly the risk of breakthrough infections, I think people are reconsidering,” she said.

For patients who have had COVID-19, there’s a simple message.

“Just because you’ve had COVID-19 and recovered from it doesn’t make you immune. You’re still at risk of getting COVID-19. Our only protection at the moment is the vaccination,” Ms Baptista advised.

Also online first at

Ethics and Law: Consent for treatment of gender dysphoria in minors: evolving clinical and legal frameworks
Ouliaris; doi: 10.5694/mja2.51357OPEN ACCESS permanently

Perspective: Patient‐reported outcome measures (PROMs) to guide clinical care: recommendations and challenges
Agarwal et al; doi: 10.5694/mja2.51355OPEN ACCESS permanently

3 thoughts on “Had COVID-19 once? Get vaccinated, says new data

  1. Anouska Dobiecki says:

    Randall and Mohamed are correct. Mild symptoms. British NHS reports 85% of positive cases are asymptomatic or mild symptoms. Primary studies on this omicron variant from Botswana and Nigeria show greater transmissibility and a lessening of symptoms. To be forced, worldwide, to take a vaccine for a disease that really only affects the elderly or already sick. Sigh.

  2. Randal says:

    “…Just because you’ve had COVID-19 and recovered from it doesn’t make you immune. You’re still at risk of getting COVID-19. Our only protection at the moment is the vaccination.”

    Huh? The vaccine also doesn’t make one immune, indeed it confers less immunity (and cross-immunity) than becoming infected. Meanwhile, re-infections are proving to be mild (as is original infection for essentially anyone without significant co-morbidities).

    Vaccination cannot lead to herd immunity — it could not unless it reduced infection rate by ~90%+, which it does not. A supposed reduction of 30% in tramissibility does not give herd protection — it merely spreads out (er, flattens) the curve, which as we have demonstrated is not necessary (remember: flattening the curve was “justified” in order to prevent hospitals from being over-run, and to buy time until…vaccines!)

    The net benefit of vaccination protection above and beyond actually becoming infected has not been quantified, or even qualified as being sufficient to argue for vaccination in those patients.

  3. Mohamed says:

    So all the individuals who were reinfected had mild symptoms only, despite not being vaccinated.

    And you think this “evidence” supports vaccination??

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