Virus-fighting antibodies have been shown to linger in Kiwi Covid-19 patients nearly a year after they were infected, in a globally unique study that could give vaccine makers a valuable benchmark.
Antibodies play a critical role in the immune system’s fight against pathogens like the coronavirus.
Upon a new virus being recognised, antibodies are specially created to bind to its “spike protein” and stop it entering our cells – all while signalling other parts of the immune system to destroy the foreign invader.
Now, new research has provided more evidence that these hang about in our bodies long after we’ve been infected by the Sars-CoV-2 virus.
A team of researchers have been tracking antibody responses using samples taken from a group of patients from Southland who were infected during New Zealand’s first wave.
In earlier work, they measured the ability of the antibodies to neutralise only the original or “ancestral” strain of the virus.
But in their latest study, the scientists also measured the antibodies against other variants of concern, including delta.
“The variants have slightly different spike proteins and we wanted to assess whether antibodies generated to an infection with the ancestral strain would also neutralise different variants,” study co-author and University of Auckland immunologist Dr Nikki Moreland said.
They later found that the specific antibodies that binded to the spike protein, along with neutralising antibodies, stayed stable for up to 11 months after infection.
“While this is a relatively small study, the fact that over 95 per cent of the participants had neutralising antibodies after this period of time is encouraging,” co-author and University of Auckland research scientist Dr Reuben McGregor said.
“Added to that, these antibodies also neutralised the spike protein of the delta variant, with only a slightly reduction compared to the ancestral strain.”
The study, published online ahead of peer review, is thought to be one of just a few that can claim to be measuring antibodies in an environment with little risk of re-exposure and boosting of the antibody response.
“This is because the study was conducted in the Southern region over a time period when there was no community transmission, thanks to our elimination strategy, and before the vaccine roll-out began,” McGregor said.
Moreland said the findings boded well for the vaccine roll-out, as it provided a benchmark for a high level of neutralising antibodies after vaccination as well.
While there are concerns that immunity induced by the Pfizer shot and other vaccines may wane over time, prompting the prospect of booster shots, Moreland said international data clearly showed the Pfizer vaccine brought on antibodies that could neutralise Delta.
Large clinical trials have shown protection against symptomatic Covid-19 to be around 52 per cent at about 12 days after the first dose of the Pfizer shot – but 95 per cent after the second dose.
More recently, “real-world” data from observations of front-line workers has put the level of protection at 62 to 91 per cent from two weeks after the first dose, and at between 68 and 97 per cent after the second.
“Although our study shows that infection can induce a long-lived antibody responses, vaccination is a much safer way to get there,” Moreland said.
“The virus can really wreak havoc on the body and with vaccination people get protection without the risk of becoming very unwell or developing long Covid.”
The study comes after another paper, led by University of Canterbury mathematician Dr Alex James, also offered some promising findings.
James and her colleagues used data from six papers to create a model that predicted antibody response in two stages: an initial peak after infection, and a relatively fast decline from this peak.
Then, the levels of antibodies essentially levelled off and the decline was much slower.
This levelling off in antibodies suggested the immune system was switching from the original response to the virus to a longer-term memory response.
When the datasets were analysed together, the model showed the initial peak lasted for about 17 days before the antibodies levelled off, and the “half-life” was 345 days.
This implied that, one to two years after infection, antibodies would be at about 23 per cent and 11 per cent of their maximum level respectively.
“This is a highly encouraging result and if vaccine immunity follows a similar pattern it gives hope that yearly or even two-yearly booster immunisations could be sufficient to provide long-lasting immunity,” James and colleagues said.
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