Australian patients with haematological and solid cancers have been well protected during the COVID-19 pandemic thanks to a “very intense vaccination strategy” a cancer meeting has been told.
Speaking to the limbic at the COSA ASM 2022, medical oncologist Dr Amy Body said she would counsel patients that three vaccination doses were essential.
“You can’t get away with two doses and probably the fourth dose is really important as well because it does boost that antibody titre further.”
However results from the SerOzNET study confirm there are still a proportion of patients who don’t mount an antibody response no matter how many doses they have.
“I think for those people, we really need to continue preventive measures like masks and protecting them in clinical areas from other patients,” she said.
Dr Body, from Monash Health, presented the results from a cohort of 510 cancer patients – 396 adults aged 20+ years and 114 children and adolescents 5-19 years – who received standard of care vaccinations as per ATAGI guidelines.
The prospective observational study, which enrolled patients from cancer centres in Melbourne, Sydney and Perth, collected blood samples at baseline and after each vaccine dose which is ongoing through to 3 months after dose 5.
About two-thirds of adults had solid cancers whereas about two-thirds of children and adolescents had haematological cancers.
Treatment types amongst adults were varied including targeted therapies and immunotherapy whereas most children and adolescents received chemotherapy. Fewer than half the adults (46%) had received chemotherapy within a year of vaccination compared to about 90% of children and adolescents.
Dr Body said 52% of the children with solid cancers and 40% of those with haematological cancers had a detectable antibody response after their first COVID-19 vaccination which then rose to 68% and 57% respectively after a second dose.
“But even after three doses … and remember most of them have had recent chemotherapy – one-fifth (19%) with solid cancer and one-third (32%) with haematological cancer do not have detectable antibody responses.”
The study found antibody responses were maintained for at least three months after a vaccine dose.
The data was backed up with significant increments in neutralising antibody titres after each dose.
“People who develop a response have similar titres regardless of cancer type,” she said.
Adults initially were less likely than younger patients to have detectable antibodies after dose 1 but this quickly incremented up to 87% of solid cancer patients and 41% of haematological patients responding after the second dose.
After a third dose, 97% of solid cancer patients and 66% of haematological cancer patients had detectable antibodies, with further slight improvements after the fourth dose.
“Again, three months after a dose, the proportion of responders is similar to one month post dose.”
Dr Body said higher measurable antibody titres were observed after each dose.
“We don’t know what the clinical significance of this is yet but it is something that we will continue looking at. Again, between solid and haematological cancers there is generally no difference except at the very early time point after the second dose when the solid cancer patients did have an improved titre.”
The study also measured T-cell interferon gamma production after each vaccine dose.
In children and adolescents, about one-third of patients did not respond between dose 1 and dose 2, but there was significant increase between the second and third dose with almost all patients having a response after that timepoint.
Dr Body said the T-cell response appeared similar between haematological and solid cancers compared to the neutralising antibody data which showed where solid cancer patients responded better,
“Similarly, in the adults, there is an incremental improvement after each dose and no significant difference between haematological cancer and solid cancer patients.”
“After the first to second dose, the improvement in response rate goes from 57% to 77% – and so a very significant improvement – and then between the second and third dose, the response rate increases from 77% to 89%.
She said patient-reported toxicity to the vaccines was similar to that observed in registration studies – mostly local injection site reactions with low levels of systemic adverse effects – and with adults slightly less affected than younger patients.
“In terms of breakthrough infections, to date 123 of patients have reported a COVID-19 infection – 15 of those have been hospitalised however no patients have needed to go to ICU and none of our patients have died from COVID-19.”
She said several patients received targeted therapies for COVID-19 but most infections occurred early and before therapies were widely available.
“The vaccine strategy in Australia has been really successful with a really low level of serious COVID-related morbidity and mortality with our intensive vaccination recommendations and despite a large number of our patients being infected we have had really minimal morbidity related to COVID amongst our cohort.”
“Interestingly, the antibody titre does incrementally improve even after a fourth dose and I think we are still working on the clinical significance of the absolute titres and whether this relates to better disease protection.”
Dr Body noted children with cancer were particularly vulnerable which was probably related to their different treatment paradigms.
“We need to address this by looking at different vaccination strategies, possibly additional doses, possibly higher doses and possibly the role of revaccination after completion of aggressive therapies and the need for other preventive measures such as ongoing mask use.”
She told the limbic it was easy to be a bit blasé with children given healthy children seem to manage COVID-19 so well.
“But less healthy children are not mounting a good response so they should be additionally protected.”
Dr Body said the question for all patients was how long they were protected and when vaccinations could stop.
“And that’s the million dollar question. Our collaborators at QIMR Berghofer have a healthy population cohort in whom they’ve looked at their vaccine response and then their response to natural infections.”
“When you get [naturally] infected it strengthens the response and broadens it to other antigens so low levels of COVID-19 circulating in the community will maintain that protection.”
Read the SerOzNET study protocol published in BMC Infectious Diseases here.