"Immunity from reinfection cannot be assumed.”

Research has shown that people who recover from Covid-19 have immunity from reinfection for up to six months. A new study by the Health Information and Quality Authority, which examined the potential for reinfection following a Covid-19 reinfection, has found that immunity is sustained for period of between two and six months. The review on the potential for reinfection was carried out at the request of the National Public Health Emergency Team in order to support its response to the pandemic. HIQA reviewed new evidence relating to the possibility of reinfection following recovery from SARS-CoV-2, as well as studies with longer follow-up looking at the duration of immunity following infection. Twenty-two studies were identified that examined the duration of antibody responses following SARS-CoV-2 infection for longer than 60 days. The maximum follow-up was 182 days in one study and mean maximum follow-up was 97 days across all studies. HIQA found that reinfections were rare with just 14 patients worldwide known to have been infected twice. In these cases, comparative whole genome sequencing demonstrated the first and second infections were from different viral strains. “New evidence has demonstrated that reinfection can occur following recovery from SARS-CoV-2 infection," Dr Máirín Ryan, HIQA’s Deputy CEO and Director of Health Technology Assessment said. "Worldwide, at least fourteen patients have been infected twice by SARS-CoV-2; these reinfections were confirmed by genetic evidence that showed the first and second infections were caused by different viral strains. It is important to remember, however, that these are rare events.” Dr Ryan added that the possibility for reinfection means that all public health advice - including hygiene and physical distancing - should apply to those who have recovered from Covid-19 as immunity cannot be assumed. “Evidence from 22 studies suggests that IgG antibody levels (the most common antibody in the blood) are sustained for at least two months after infection, and for some even up to six months," Dr Ryan said. "The levels of neutralising antibodies (that can neutralise viruses like SARS-CoV-2), decline over time, especially in the later stages of follow-up. While this doesn’t offer a full picture of the body’s response to SARS-CoV-2, these data have implications for vaccine development, antibody testing and immunotherapy going forward.”