Another study has shown that immunity to Covid in those who have been infected and recovered is long-lasting, “broad and effective” – raising questions about the Irish government’s decision to limit recovery certificates to just six months after being tested positive for the virus.
A new paper published as a preprint in the scientific journal Cell found that a longitudinal analysis shows “durable and broad immune memory” after an infection with Covid-19 “with persisting antibody responses and memory B and T cells”.
The study found that long-lasting immunity was conferred even when patients had only had a mild infection of Covid-19.
“This in-depth longitudinal study demonstrates that durable immune memory persists in most COVID-19 patients, including those with mild disease, and serves as a framework to define and predict long-lived immunity to SARS-CoV-2 after natural infection,” researchers said.
That means that those who have recovered from Covid-19, perhaps numbering up to half a million people in Ireland if asymptomatic cases are included, have long-lasting immunity.
“Ending the COVID-19 pandemic will require long-lived immunity to SARS-CoV-2,” the authors of the new study say, explaining that they evaluated 254 Covid-19 patients for up to 8 months and found that lasting protection was conferred from having previously been infected with the virus.
They explained that samples taken after 250 days revealed a slowing of antibody decay towards a plateau level, indicating the generation of longer-lived plasma cells and more durable antibody responses, which would point to a long-lasting protection to those who are Covid-recovered.
Moreover, they took aim at the “notion” that immunity conferred after recovery from Covid-19 might be short-lived, saying that the investigation showed the generation of long-lived plasma cells and “refute the current notion that these antibody responses to human coronaviruses are short lived.”
They also found that COVID-19 patients mounted increased antibody responses to another coronavirus, “SARS-CoV-1, a related pathogen that none likely had experienced previous exposure to.”
The study noted that “the COVID-19 pandemic remains a global public health threat after 1 year of overwhelming disruption and loss. Overcoming the challenges to end the pandemic is accentuated by the recognition that SARS-CoV-2 can undergo rapid antigenic variation that may lower vaccine effectiveness in preventing new cases and progression to severe disease.”
With that in mind, their findings that Covid-19 patients induced a “wide-ranging immune defense” which would also be likely to “provide some degree of protective immunity” even against variants, is significant.
The finding comes after an additional recent study, also a preprint, concluded that people who had already been infected with the coronavirus were “unlikely to benefit from COVID-19 vaccination”.
Instead, the study found, “vaccines can be safely prioritized to those who have not been infected before”.
The research, entitled “necessity of COVID-19 vaccination in previously infected individuals,” sought to evaluate the necessity of vaccination in persons previously infected with the virus. 52,238 health employees in Ohio were included in the study and the incidence of Covid-19 infection over five months among previously infected subjects who received the vaccine, was compared with those of previously infected subjects who remained unvaccinated, previously uninfected subjects who received the vaccine, and previously uninfected subjects who remained unvaccinated.
The results showed that the cumulative incidence of Covid-19 infection was almost non-existent for those who had been previously infected – as it did for those who were vaccinated.
It remained “almost zero among previously infected unvaccinated subjects, previously infected subjects who were vaccinated, and previously uninfected subjects who were vaccinated, compared with a steady increase in cumulative incidence among previously uninfected subjects who remained unvaccinated,” the paper said.
“Not one of the 1359 previously infected subjects who remained unvaccinated had a SARS-CoV-2 infection over the duration of the study,” researchers wrote.
Research published in January in Science also found that “the immune systems of more than 95% of people who recovered from COVID-19 had durable memories of the virus up to eight months after infection”.
While eight months was the longest period the study could speak to (since the Covid-19 virus only emerged last year) the results of the study indicated that immunity after infection was being conferred for years and perhaps decades.
Researchers found the immune responses remained strong in the majority of people studied – with antibody levels remaining stable over time, and the levels of other protective B and T cells increasing.
“Several months ago, our studies showed that natural infection induced a strong response, and this study now shows that the responses last,” Drs. Daniela Weiskopf who co-led the study said.
“That amount of memory would likely prevent the vast majority of people from getting hospitalized disease, severe disease, for many years,” Shane Crotty, a virologist at the La Jolla Institute of Immunology who co-authored the study told the New York Times, who described the research as the “most comprehensive and long-ranging study of immune memory to the coronavirus to date”.