A team of scientists, including some from the Danish Department of Infectious Disease Epidemiology and Prevention, noted that most people who had Covid-19 appeared to have protection against reinfection for about six months. But a check of the demographics of those who became reinfected showed that it was mostly people 65 and older.
They looked at the re-infection rate among 4 million people during the second wave of Covid-19 from September through December 31, and compared it with the infection rate during the first wave between March and May. Of the 11,068 people who tested positive during the first peak, only 72 retested positive during the second.
The older age group had only about 47% protection against re-infection, compared to younger people who seemed to have about 80% protection against reinfection, the team wrote. The finding is not entirely unexpected, because as people age, their immune systems weaken.
“Given what is at stake, the results highlight the importance of people adhering to measures implemented to protect themselves and others, even if they have already had COVID-19,” study co-author Dr. Steen Ethelberg of the Statens Serum. Institut in Denmark said in a statement.
“That’s a really big difference,” said Dr. Amy Edwards, an infectious disease specialist at university hospitals in Cleveland, who was not involved in the study.
“I think it really highlights the importance of making sure we vaccinate everyone over 60, whether they have had Covid or not, to protect them from future infections.”
In a commentary accompanying the study, immunologists named Dr. Rosemary Boyton and Daniel Altmann of Imperial College London make the difference in re-infection rate “relatively alarming”.
“Just 80% protection against reinfection in general, decreasing to 47% in people 65 and older, are more troubling figures than provided by previous studies,” they wrote. SARS-CoV-2 The hope of protective immunity from natural infections may not be within our reach, and a global vaccination program with highly effective vaccines is the sustainable solution. “
The researchers analyzed test data from Denmark related to 10.6 million coronavirus tests conducted by about 4 million people, or about 69% of the country’s population.
They looked at re-infection rates during the second wave of Covid-19 from September to December 31, and compared them to the infection rates during the first wave of infection between March and May. Of the 11,068 people who tested positive during the first peak, only 72 retested positive during the second. That amounts to less than 1% of those infected.
Only 3.6% of people 65 and older became reinfected in the second wave.
This is not unexpected, because of what is known as immunosesescence – the gradual deterioration of the immune system that comes with age.
“There is a reason why people over 60 should receive additional vaccines to boost their immunity against various infections, because we know that the immune system starts to decline later in life,” Edwards said.
A nice thing about the mRNA vaccines, like those from Pfizer and Moderna, Edwards said, is that the vaccines seem to overcome some of the immunosecence problems because they produce such robust protection.
“We just don’t know yet whether people need boosters or not, but it will be interesting to see that and how that turns out,” Edwards said.
A limitation of the study is that infections were looked at before many variants were in circulation, so it’s unclear what impact that might have on re-infection rates. That is something scientists should look at in the future.