Researchers tested 12,180 frontline health-care workers for coronavirus antibodies to see if they have been previously infected.
The researchers explained in their study that T cells regulate the activity of the immune system by recognising specific viruses.
During the study, 89 of 11,052 staff without antibodies developed a new infection with symptoms, while none of the 1,246 staff with antibodies developed a symptomatic infection. And it is likely to be even higher now that the country has experienced a second wave of infections.
It's a welcome shift from a large pool of studies that have suggested that antibodies fade within three months.
They found that while T cells were markedly activated in the lungs of patients with severe pneumonia, the T cell braking function stopped working.
Much of the scepticism was focused on the so-called specificity of the antibody tests, that, if not ideal, might reveal the presence of antibodies to other diseases.
And the T cells - the immune component that both kills off cells that have been infected and helps B cells make antibodies - stuck around for six months, and behaved the way immune cells people develop after getting yellow fever vaccines do. As well, scientists have yet to determine how T cell responses differ depending on disease severity (mild or asymptomatic versus severe or long COVID), and whether genetic factors, such as a patient's HLA type, could influence disease severity.
COVID-19 immunity can last more than six months – Study
"This is really good news, because we can be confident that, at least in the short term, most people who get COVID-19 won't get it again".
Neighbouring Victoria, which for months fought the pandemic and where 90% of Australia's 907 coronavirus-related deaths have been recorded, relaxed its mask rules on Sunday, saying they are not required outside, and allowed larger public gatherings. A small number of recovered participants did not have long-lasting immunity. That means it will reduce the viral load in the body, but also even if virus particles are passed on to another person via a sneeze or cough, that person is less likely to be infected by active virus particles.
But Dr Wrighton-Smith added: 'We are not picking up all cases with the antibody surveys - so more people may be protected than we thought'.
According to the website of the World Health Organization, as of November 12, there were 212 COVID-19 candidate vaccines being developed worldwide, and 48 of them were in clinical trials.
The scientists believe a more detailed understanding of the pathogenesis based on this research may contribute to the development of drugs to prevent the development of severe COVID-19.
They said the results are only relevant for the period of self-isolation for people with confirmed COVID-19, and do not apply to people quarantining who may or may not have been exposed after contact with someone infected.
'T-cells have been overlooked for too long.
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