‘Hybrid immunity’ enough to protect healthcare workers: DoH

Matt Woodley

27/06/2022 4:44:05 PM

New advice indicates there is not enough evidence to support offering healthcare workers a fourth ‘winter dose’.

Nurse receiving a COVID vaccine.
Hybrid immunity appears to produce strong and durable protection against future infections, and severe disease and death.

The Department of Health has sent out updated advice on the decision to not offer healthcare workers a fourth ‘winter dose’, suggesting there is insufficient evidence to support such a move.
The advice reiterates that the primary goal of the COVID-19 vaccination program is to ‘minimise the risk of severe disease including hospitalisation and death’, and that otherwise healthy people typically retain good protection against severe illness several months out from their first booster dose.
It also notes that current vaccines have only ‘limited protection against transmission’ of the Omicron strain, but retain strong protection against severe COVID-19.
This reasoning, combined with studies suggesting that healthcare workers have a greater risk of acquiring COVID-19 in community settings than through exposure at work, also underpinned the department’s advice last time questions were asked around GP access to fourth doses.
At the time, 84% of respondents to a newsGP weekly poll said all healthcare workers should have the option of receiving a winter dose, while even fewer – 7% – voted against any form of access for this cohort.
However, a review into ‘hybrid immunity’ conducted by the Australian Technical Advisory Group on Immunisation (ATAGI) should provide further reassurance to healthcare workers, the department says.
‘Those who have had a confirmed case of COVID-19 should be reassured that hybrid immunity – that is protection from a combination of vaccination and infection – appears to produce strong and durable protection against future infections, and severe disease and death,’ ATAGI states.
To support its assessment, the advisory group referenced two documents.
The first, published in Nature Reviews Immunology, draws on data from when Delta was the dominant variant of concern.
It found that protection was ‘significantly greater’ in vaccinated individuals with evidence of prior infection than those without prior infection, while people who had received one or two doses of vaccine following natural infection were also much more protected than those with natural infection alone.
ATAGI’s review of the study goes on to say that while transmission prevention has focused on neutralising antibodies due to their potential to prevent viral entry into cells and stop infection, T cells may also play an important role in protecting against severe disease.
‘These [findings] are reinforced by observations that the decline in vaccine effectiveness parallels the drop in serum neutralising antibody titres, but maintained protection against severe COVID-19 and slower waning associated with persistence of peripheral SARS-CoV-2 T cells,’ the advice states.
‘T cells may maintain the ability to protect against severe disease from VOC [variants of concern] due to the fact mutations appear to largely spare T cell epitopes.
‘Generating robust immunity to SARS-CoV-2 in the future is a priority in case new VOC emerge. In the short-term, this is likely to involve harnessing the power of hybrid immunity to optimise the use of existing vaccines.’
The second document cited by ATAGI is the World Health Organization’s (WHO) interim statement on hybrid immunity and increasing population seroprevalence rates.
According to the WHO statement, most studies have found that protection conferred by hybrid immunity against infection and mild symptomatic disease is similar or modestly better than infection- or vaccine-induced immunity alone.
It also indicates that a combination of both vaccination and natural infection is more likely to offer superior protection against severe disease, including death.
‘Hybrid immunity resulting from three or more exposures to the virus antigen [ie, one or more exposures from vaccination and one or more from SARS-CoV-2 infections before or after vaccination] may provide superior protection [as measured by neutralisation capacity] against VOCs, including Omicron, compared with two doses of vaccination, or previous SARS-CoV-2 infection without vaccination,’ the WHO states.
However, it also states that the waning of hybrid immunity, particularly due to Omicron infections, is ‘not yet characterised in magnitude or duration’.
The WHO statement goes on to say that the optimal timing of the primary vaccination course and booster doses ‘may differ’ according to whether individuals have had a previous SARS-CoV-2 infection.
‘Any policy regarding the vaccination of lower priority use groups should involve clear specification of the value of vaccination under consideration and multiple trade-offs, with seroprevalence in these groups representing one of the factors to be considered in the future,’ the WHO states.
Limited benefit
ATAGI concluded its assessment by suggesting that while breakthrough protection after vaccination (or vaccination post infection) results in a boost of antibody levels, current data suggest additional doses in the setting of hybrid immunity ‘does not result in significantly increased antibody levels’.
‘Although there is no correlate of protection, this current data suggest limited benefit of additional doses,’ ATAGI stated.
However, it also left open the possibility of updating this advice should circumstances change.
‘ATAGI recognises that in the context of very high rates of COVID-19 circulation, vaccination of additional groups at lower risk of severe disease may be warranted in the future to prevent milder infection and reduce transmission in the short-term,’ it said.
‘ATAGI will continue to monitor disease modelling and the epidemiology of COVID-19 and may recommend wider vaccination to combat rapid increases in disease transmission in the future if the need arises.’
An ongoing review of evidence, including from countries that have rolled out an additional booster doses for certain professional groups, will continue to inform the group’s advice in relation to a fourth dose.
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ATAGI COVID-19 Department of Health hybrid immunity natural infection Omicron World Health Organization

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Dr Ian   28/06/2022 5:44:01 AM

The policy of not offering the second booster to general practice is not adressing the incidence of post covid in mild to moderate infections or the immune escape ability of Omicron BA4 and BA 5 . Not only that but past infections are not as protective for Omicron subvariants and second and third infections are occuring with some maintaining that second and third infections can worsen damage and post covid . Futher there are many General Practitioners and Staff older than 50 and with co-morbidity , The RACGP winter plan is recommending offering staff serological tests for antibodies to spike and nucleocapsid antigen a sign of doubts about the extensiveness of protection for some health staff exposed to omicron Covid .

DrMT   28/06/2022 6:17:12 AM

Does that mean DoH now encourages people to have “Hybrid immunity”? The idea of “Herd immunity” was strongly opposed at the beginning and during the pandemic. Nobody wants to get Covid infection as you can never predict what it does to your health long term (post Covid). Most GPs are under 65yo and can not get access to Antiviral treatment. Most GPs have 3rd booster more than 6 months ago, the immunity waned. Protection, prevention are still more important than “hybrid immunity”. 4th booster should be offered to GPs who are front line workers and have high risks of exposure to patients with Covid everyday

Dr Michelle Johnston   28/06/2022 9:21:58 AM

Denying health workers a 4th dose seems to ignore those of us that have managed to avoid covid so far and do not have hybrid immunity. I would much prefer a booster to infection. Should we not at least be offered this choice?

Rural GP   28/06/2022 6:07:33 PM

Our GP's (above) make valid really valid comments. Its a patronising " pat on the head" for the cannon fodder. No recognition that we can make our own decisions, or represent other healthcare workers. Remember, the DoH says we don't know how to read an ECG? ....This is just a guideline.

Dr Helen Demetriou   29/06/2022 2:46:07 PM

Fully vaccinated currently in iso with my second covid infection 4 weeks after my first. I’m very fit under 50 with no health issues so beg to differ on this one. Might not be a gp workforce available to see patients at this rate…..

Dr Mark Miller   30/06/2022 12:55:49 AM

Reactivity vs pro-activity, most GPs spend their lives trying to prevent chronic illness proactivley but required to deal reactively to external policy.

Israel decided in early January 22, in light of the rapid spread of Omicron, vaccination of older adults aged 60 and older, individuals at high risk and medical teams with the fourth vaccine dose was initiated. Preliminary data analysis tested the effectiveness of the fourth vaccine dose found that among adults aged 60 and older, the fourth dose raises protection against infection by up to 2 times, compared to those previously-vaccinated with the third dose. Additionally, the fourth dose raises protection against severe illness by up to 3 times and higher compared to those previously-vaccinated with the third dose.