Woman’s two Covid-19 infections in 21 days highlight need for vigilance
The experience of a woman in Spain who tested positive for coronavirus twice in three weeks has underlined the importance of guarding against complacency after infection.
The healthcare worker, 31, returned a positive PCR test result on December 20, 12 days after receiving a booster shot.
She was asymptomatic at the time and remained so throughout the infection.
But on January 10 she began to feel unwell with a cough and fever. She took another PCR test, which was positive.
Genome sequencing performed on her samples showed she had been infected by different variants, researchers said.
The first infection was with Delta but the second was with Omicron, which went on to become the dominant Covid-19 variant worldwide.
Although considered milder than previous coronavirus variants, it can evade previous immunity and is more infectious.
Researchers who studied the woman’s case said it showed how Omicron can evade antibodies generated by vaccines and previous infections.
“In other words, people who have had Covid-19 cannot assume they are protected against reinfection, even if they have been fully vaccinated,” said Dr Gemma Recio, of the Catalan Institute of Health.
“Nevertheless, both previous infection with other variants and vaccination do seem to partially protect against severe disease and hospitalisation in those with Omicron.
“This case also underscores the need to carry out genomic surveillance of viruses in infections in those who are fully vaccinated, and in reinfections.
“Such monitoring will help detect variants with the ability to partially evade the immune response.”
Many countries, including the UK, count reinfections only after 90 days.
But they are fairly common, representing one in 10 Covid-19 cases in England in early this month the UK’s Office for National Statistics said.
Half of all reinfections in the UK have occurred since December 1, suggesting the risk rose substantially with Omicron.
Primary infections after vaccination are milder than in people who have not had a shot.
For that reason, it is reasonable to assume that, in general, “reinfections should be less severe than primary infections, as the person being reinfected will have some pre-existing immunity from their primary infection,” according to an information page on reinfections by Gavi, the Vaccine Alliance.
But whether a person develops more or fewer symptoms during reinfection depends on several factors, including the variant involved. The ONS says only 20 per cent of people reinfected with the Alpha strain show symptoms.
With Delta it was 44 per cent and when it came to cases with Omicron, 46 per cent of people developed symptoms.
The data revealed people reinfected with Alpha were far less likely to have symptoms the second time compared with during their primary infection.
“Delta reinfections were somewhat more likely to give people symptoms compared with their primary infection,” Gavi said.
“With an Omicron reinfection, the rate of symptoms was about the same across the reinfection and primary infection.”
In one study of Omicron infection and reinfection in a US household cited by the Centres for Disease Control and Prevention, and Gavi, one unvaccinated person caught the virus for the first time and four unvaccinated people for a second time.
The severity of the illness was worse for the person who caught it for the first time, compared with those who were reinfected with Omicron.
“On the other hand, there have been opposing reports in the past of more severe disease being caused by reinfection,” Gavi said.
“So, while it’s plausible that reinfections should be milder, at the moment, we’re still lacking robust evidence that proves this.”
Factors such as viral load may also play a role, with many studies having previously shown that a higher initial dose of the virus leads to more severe symptoms.