Research conducted by Oxford University and UK Coronavirus Immunology Consortium showed that the previous coronavirus infection does not necessarily offer protection against Covid in the longer duration, especially when caused by new variants of concern.
This study, first reported by The Guardian, was conducted on health workers found distinct differences in the immune responses of medical staff who got infected with Covid, some appearing better equipped than others to fight the disease six months later.
Scientists said that the findings highlighted the importance of getting vaccinated irrespective of whether people had been infected with the virus earlier than the pandemic.
“If you look at the trajectory of the immune response after infection, mostly it is still detectable six months later, but it’s highly variable between people,” said Eleanor Barnes, a professor of hepatology and experimental medicine at Oxford and a senior author on the study.
“That is quite different from vaccination. If you vaccinate you get a really robust response, but with natural infection there’s much more diversity in responses”, she added.
The research team analysed blood samples of 78 healthcare workers who had Covid, with or without symptoms, between April and June last year. The blood was checked for six months post-infection to record a range of immune responses.
Most people who had a weak immune response at one month had no detectable antibodies to neutralise the Alpha variant, first seen in Kent, at six months. None showed neutralising antibodies against the Beta variant first spotted in South Africa. The researchers are yet to analyse data for the Delta variant now dominant in the UK.
Majority of healthcare workers who developed symptomatic disease showed a measurable immune response six months later, more than a quarter did not. The researchers also found that more than 90% of people who had asymptomatic infections had no measurable immune response six months later.
“In our view, previous infection does not necessarily protect you long-term from Sars-Cov-2, particularly variants of concern,” said Barnes. “You shouldn’t depend on it to protect you from subsequent disease, you should be vaccinated.
Danny Altmann, a professor of immunology at Imperial College London, said,“People show rather diverse trajectories after infection, but immunity often seems to hold up well at six months,” he said. “Most of all, studies such as this remind us that policy decisions on ‘boosting’ need to be evidence based in the context of a strong programme of immune monitoring.”