Regular boosters may be needed for a vaccine against Covid-19 due to people’s antibody response to the disease declining over time, new information provided to the National Public Health Emergency Team (Nphet) states.
A Health Information and Quality Authority (Hiqa) reports says Covid-19 immunity can last for between two and six months after infection and that while rare, reinfection is possible.
At least 14 patients worldwide have been reinfected by SARS-CoV-2, the virus that causes Covid-19, research based on genetic evidence that showed the first and second infections were caused by different viral strains has found.
Dr Máirín Ryan, Hiqa’s deputy chief executive, said the fact that reinfection happens has significant policy implications, with the same need for infection controls, isolation and contact tracing as in first-time cases.
“All public health advice, including hygiene and physical distancing, should apply to those who have recovered from a SARS-CoV-2 infection as immunity from reinfection cannot be assumed,” she said.
Evidence from 22 studies suggests IgG antibody levels (the most common antibody in the blood) are sustained for at least two months after infection and for up to six months in some people. Levels of antibodies that can neutralise viruses decline over time.
Dr Ryan said this has implications for vaccine development, antibody testing and immunotherapy.
Many of the Covid-19 vaccines currently in development focus on generating a strong neutralising antibody response to provide protection from infection.
Hiqa said its findings suggest immunity may not be long-term and if vaccination results in a similar response, “consideration may be given to the need for repeat of ‘booster’ doses”. It has also found limited evidence that convalescent plasma is an effective treatment for Covid-19, with low rates of adverse events.
Convalescent plasma from patients recently recovered from a disease contains antibodies which, when transfused into others, may provide passive immunity to the disease in recipients. Historically, it has been used to treat conditions for which there was no vaccine or drug intervention.
“In cases where there are no other alternative treatments available, convalescent plasma may offer a potential treatment option for (Covid-19) patients at high risk of a severe course of the disease,” Hiqa said.