Although uncommon, COVID-19 reinfections do occur, especially in people aged 65 and over, underscoring the importance of continuous physical detachment and prioritizing vaccines even in previously infected people, a large observational study yesterday in The Lancet suggests.
Researchers at the Statens Serum Institut in Copenhagen, Denmark, analyzed data from 10.6 million SARS-CoV-2 tests from 4 million Danes (69% of the population) from that country’s second COVID-19 peak, from September 1 to December 31, 2020. They then compared them to the infection rates of residents with positive or negative tests during the first outbreak, from March to May 2020.
Before June 2020, 533,381 residents were tested, of which 2.20% were positive for COVID-19. Of the 525,339 people eligible for follow-up during the second wave, 2.11% were infected during the first wave and 0.65% tested positive again. In comparison, 3.27% of the 514,271 who tested negative during the first wave were infected (adjusted relative risk [aRR], 0.195). Protection against reinfection was 80.5%.
An alternative cohort analysis of COVID-19 infection rates over the year in those with a previous infection versus one without 3 months before or more generated similar estimates (aRR, 0.212), for a 78.8% protection. Among residents aged 65 and over, however, the protection seen against reinfection was only 47.1%.
Older people, the researchers said, may be more likely to be reinfected due to decreased age-related immunity, disrupted coordination of coronavirus-specific T-cell responses and scarcity of virgin T-cells, which have been associated with aging and poor COVID – 19 results.
‘Natural protection cannot be trusted’
There was no difference in the estimated protection against reinfection by sex (78.4% in men vs 79.1% in women) or evidence of protection from weakening over time (79.3% in 3 to 6 months of follow-up vs 77, 7% in 7 months of follow-up or more). The study involved only the original coronavirus strain; the variants have not been evaluated.
In a sensitivity analysis of a sample restricted to 15,604 doctors, nurses, social workers and health workers, who were tested at a median of 10 times in 2020, 658 (4.2%) of whom tested positive during the first outbreak . Of those 658, 1.2% were reinfected during the second wave, compared with 6.2% of those who tested negative during the first wave (aRR, 0.189; estimated protection against repeated infection, 81.1%).
“As the older age group is more prone to a serious clinical course of the disease, this finding highlights the need to implement protective measures for the older population in the form of effective vaccines and greater physical distance and infection control, even in those who are known to be previously infected “, they wrote.
The study’s co-author, Steen Ethelberg, PhD, said in a Lancet press release that their findings may inform policies on vaccination strategies and the relaxation of public health restrictions. “As the elderly are also more likely to have severe symptoms of illness and, unfortunately, to die, our findings make it clear how important it is to implement policies to protect the elderly during the pandemic,” he said.
The authors said that a better understanding of the degree and duration of protection, as well as the mechanisms of immunity, against recurrent coronavirus infection is critical to formulating optimal intervention strategies. “Our data indicate that vaccination of previously infected individuals should be done because natural protection cannot be relied on,” they wrote.
The launch calls it the first large-scale study of its kind.
Vaccination is a ‘lasting solution’
In a commentary in the same newspaper, Rosemary Boyton, MBBS and Daniel Altmann, PhD, of Imperial College London, said the quality and durability of the protection produced by natural COVID-19 infection is weaker than the highest concentrations of neutralizing antibodies generated by currently available vaccines – a discovery complicated by coronavirus variants capable of escaping the vaccine-induced natural immune response.
“Interestingly, responses to the vaccine, even after a single dose, are substantially increased in individuals with a history of SARS-CoV-2 infection,” they said. “All of this data is confirmation, if necessary, that for SARS-CoV-2 the hope of protective immunity through natural infections may not be within reach, and a global vaccination program with highly effective vaccines is the lasting solution. “