Hiqa says immunity can last between two and six months after virus but reinfection is rare
Paul Cullen Health Editor, Irish Times
Many of the Covid-19 vaccines currently in development focus on generating a strong neutralising antibody response to provide protection from infection.
Regular boosters may be needed for a vaccine against Covid-19 due to declining antibody response over time, according to new evidence provided to the National Public Health Emergency Team (Nphet).
Immunity can last between two and six months after infection with the virus, and re-infection is rare but possible, according to the advice from the Health Information and Quality Authority (Hiqa).
Worldwide, at least 14 patients have been re-infected by SARS-CoV-2, the virus that causes Covid-19, according to research based on 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,” said Dr Máirín Ryan, Hiqa’s deputy chief executive and director of health technology assessment.
The fact that re-infection happens has significant policy implications, she warned, with the same infection control, isolation and contact tracing requirements applying to the re-infection as with the first infection.
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 some up to six months. Levels of bodies that can neutralised viruses decline over time, especially in the later stages.
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”.
Hiqa has also found limited evidence that convalescent plasma is an effective treatment for Covid-19, with low rates of adverse events.
“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.