A team of scientists, including some from the Department of Epidemiology and Infectious Disease Prevention in Denmark, noted that most people who contracted Covid-19 appeared to be protected from reinfection which had remained stable for more than six months. At follow-up after six months, the study found no evidence of diminished protection. But examining the demographics of those who were infected again showed that most of them were people aged 65 or older.
They studied the rate of re-infection among 4 million people during the second wave of Covid-19 from September through December 31, and compared this to the rate of infection during the first increase between March and May. Of the 11,068 people who tested positive for the virus during the first increase, only 72 people tested positive again within the second.
The team wrote that the older age group only had 47% protection against re-infection, compared to younger people who appeared to have 80% protection from reinfection. This finding is not entirely unexpected, as their immune system weakens with age.
“Looking at what is at stake, the findings underscore how important it is for people to adhere to the measures that have been implemented to keep themselves and others safe, even if they already have COVID-19,” said study co-author Dr. Steen Ethelberg of Statens Serum, the institute said at Denmark in a statement.
“That’s a very stark difference,” said Dr. Amy Edwards, an infectious disease specialist at University Hospitals of Cleveland, who was not involved in the study.
“I think it really underlines how important it is to make sure everyone over the age of 60 is vaccinated, whether or not they have Covid, to protect them from infection in the future.”
In a commentary that coincided with the study, immunologists Dr. Rosemary Boyton and Daniel Altmann of Imperial College London described the difference in the rate of reinfection as “relatively worrying”.
They write: “Only 80% of re-infection protection overall, which drops to 47% in people 65 or older, are even more worrying numbers than those presented by previous studies.” SARS-CoV-2, Hope for preventive immunity through natural infection may not be within our grasp, and a global vaccination program with highly effective vaccines is a permanent solution. “
The researchers analyzed test data from Denmark that included 10.6 million coronavirus tests conducted by about 4 million people, or about 69% of the country’s population.
They looked at infection rates again during the second wave of Covid-19 from September through December 31, and compared them to infection rates during the first wave of infection between March and May. Of the 11,068 people who tested positive for the virus during the first increase, only 72 people tested positive again within the second. This adds up to less than 1% of those infected.
But 3.6% of people age 65 or older were infected again in the second wave
This is not unexpected, due to what is known as immune swelling – the gradual deterioration of the immune system that comes with age.
“There is a reason why people over the age of 60 need to get additional vaccines to boost their immunity against various infections, because we know that the immune system begins to decline later in life,” Edwards said.
One of the nice things about mRNA vaccines, like Pfizer and Moderna, is that vaccines seem to overcome some immunity concerns because they produce such powerful protections, Edwards said.
“We don’t know yet if people will need a boost or not,” Edwards said, “but it will be interesting to watch and see how that will happen.”
One limitation of the study is that it looked at infection before there were too many variables in circulation, so it is unclear what effect this would have on the rate of reinfection. This is something that scientists should consider going forward.