The first scientist-confirmed Irish case of a person being infected twice by Covid-19 has been reported in a 40-year-old healthcare worker who caught the virus in April and November 2020.
The woman first presented with fever, headache, sore throat, shortness of breath and the loss of sense of taste, resulting in her missing work for four weeks due to significant headaches and persistent fatigue lasting four months, according to a paper published in the Irish Medical Journal.
Seven months later, she presented again with Covid-19 suffering from a cough, headache, sore throat, fatigue and muscle pain. The second occurrence was milder and she recovered quickly, remaining off work for a two-week period in self-isolation.
"To our knowledge, this is the first report of reinfection from Ireland, " said the scientists who authored the report, including Cillian De Gascun, the director of UCD's National Virus Reference Laboratory and a member of the State's National Public Health Emergency Team.
Dr De Gascun told The Irish Times that this was the first reported in literature and confirmed with whole genome sequencing, the comprehensive testing that tracks variants.
He said that it was “very unlikely” that it was “actually the first case of reinfection”.
Previously infected people have become reinfected by Covid-19 through the different waves of the pandemic, though the rate of reinfection remains rare.
Data from the HSE’s Health Protection Surveillance Centre in March showed that out of 232,738 confirmed cases of the disease notified over the previous 12 months, some 514, or 0.2 per cent of all cases, were potential reinfections.
Public health investigators have detected reinfection cases on a weekly basis since the second half of last year. Reinfections became more common during the third wave of the virus around Christmas as some people became infected with Covid-19 for a second time by the more transmissible B117 variant first discovered in the UK last autumn.
In its latest letter to Government, Nphet urged unvaccinated people to be careful, limit indoor interactions with other unvaccinated people and avoid crowded indoor situations. Nphet warned that depending on the transmissibility of the B117 variant, there could still be a spike in cases. Dr Tony Holohan also said Nphet had endorsed Hiqa advice extending presumptive immunity from six to nine months post-infection.
Dr Anne Moore, vaccine specialist at UCC's school of biochemistry, said that the risk of reinfection comes down to how little immunity a person needs to be protected against a current or new variant.
“You don’t need much to be protected, which is why you don’t see many cases of reinfection because even with a low level of immunity, you are still protected from reinfection,” she said.
She said there was now "a race" between vaccinating people fully and new variants that could evade vaccine-induced immunity. She warned a semi-vaccinated population was "fertile land" for new variants to adapt and become more virulent when data from the UK showed that a first vaccine dose was just 33 per cent effective against the more transmissible B1617.2 variant now circulating in England.
“There is a risk there will be a new variant that will overcome pre-existing immunity induced either through vaccination or infection, which is why we need vaccines that protect against any possible coronavirus and why there is this discussion about boosters,” said Dr Moore.
In a Twitter thread on Tuesday, Dr De Gascun said the public health officials were concerned about vaccine effectiveness against the B1617.2 variant, first detected in India, because two doses would be required "to optimise effectiveness".
He said that there was concern in Ireland about this more transmissible variant of the virus at a time when a large proportion of the Irish population were still not fully vaccinated with two doses and there was an increase in social contacts associated with the easing of restrictions.