Covid-19 coronavirus: Cases raise questions of whether we should adapt our approach

There have been three known cases so far of people becoming reinfected with the coronavirus. Photo / AP

Why is the Hong Kong case significant?

Experts have been waiting for hard data to show whether people can be reinfected with Covid-19, as is the case in other coronaviruses such as the common cold. Previous cases of reinfection have been down to either the virus lingering in the body or false negative tests. Genetic analysis shows that the two samples were different "clades" or strains of the disease. The first, taken on March 26, was closely related to strains collected in the US and England in March and April, while the second, taken on August 15, was linked to strains collected in Switzerland and England in the northern summer. Today two other cases of reinfection were reported - in the Netherlands and Belgium.

Does this mean there are likely to be other cases of reinfection that we don't know about?

Scientists say that with more than 23 million cases of coronavirus now reported globally, cases of reinfection are not unusual. But Dr Margaret Harris, of the World Health Organisation, told the BBC: "We would expect that given the quality of the surveillance - and the study in Hong Kong shows what a high level of surveillance they are doing there - you would have expected to see many more cases if this was happening a lot."

What implications does this have for immunity to Covid-19?

Antibody studies have indicated that immunity to the virus may wane over time, and this study seems to confirm this. However, while initial exposure to the virus may not give you absolute protection, it may mean "that subsequent infections may be milder than the first, as for this patient," the researchers said.

Will this change our approach to vaccines?

Dr David Strain, clinical senior lecturer at the University of Exeter, said the cases suggests that vaccinations may not provide the hope we have been waiting for. "Vaccinations work by simulating infection to the body, allowing it to develop antibodies. If antibodies don't provide lasting protection, we'll need to revert to a strategy of viral near-elimination in order to return to a more normal life." The experts behind the Oxford vaccine - seen as the front-runner in the race for a jab - have said people may need an annual booster, similar to the flu jab. The case also shows that people who have had coronavirus should also be included in any vaccination programmes.

Does this mean the virus has mutated into different strains?

Viruses mutate all the time, and the fact that the genetic sequences of the Hong Kong samples were different does not mean the virus has changed significantly. Dr Simon Clarke, associate professor in cellular microbiology at the University of Reading, said: "A mutant strain is nothing to be surprised by. It would be more interesting if there were no mutations cropping up."