The research was conducted in Denmark and published in The Lancet
Madrid El País reported that the largest study to date on the risk of coronavirus reinfection showed that in the first wave of infection, only 0.65% of people were reinfected in the second wave.
Studies have also confirmed that natural immunity can last at least six months without significantly weakening. However, in people over 65 years of age, the degree of protection seems to be lower.
Several works have been published, at the risk that the infected person may be infected again. Almost all the respondents did not exceed 1%, but their survey subjects were a small number and the time frame was very short.
However, researchers at the Danish Center for Disease Control, the Stanton Serum Institute (SSI), used a large-scale PCR technology program developed by the Danish government to determine how many people were infected with the virus again. In the country, the test is free and all citizens can take it, regardless of whether they have symptoms or not.
Of the hundreds of PCRs they can perform in February, they continue to test 10% of the 5.8 million residents every week. As of December 31, 2020, when the study was completed, more than two-thirds of the population had received at least one inspection, and half of Danes had received two or more inspections.
The study just published in the medical journal The Lancet showed that 0.65% of those who tested positive in the first wave (February to May) were in the second wave (September to December). ) Recovered to CRP positive.
The difference between the two waves is to determine that the distance between infection and reinfection is at least three months. As a result, they reduce the risk that the so-called re-infected person is actually an infected person, who continues to be positive for several weeks after the first test. By the way, they did not find any cases of triple infection.
The study’s lead author, SSI epidemiologist Steen Ethelberg, said in a note that his work confirms “other recommendations: healthy young people rarely get Covid again, but older people are at higher risk of re-infection. .”.
Indeed, not only have the identity of the person who has performed PCR and their results, but also the ability to conduct continuous testing, they can estimate that the protection rate for at least six months remains around 80%. However, they found that among people over 65, this proportion dropped to 47%.
Esselberg also admitted that their research may contain some biases that distort the percentage of reinfections they observe.
For example, those who have tested positive in the first wave may be less interested in the second round of PCR and “think they are immune.” But this will be offset by those who can relax protective measures after being active. Both possibilities will be offset, thereby reducing their impact on the overall result.
The study author conducted a specific analysis to confirm the validity of his conclusions. They reviewed one of them and tested more than 15,000 health workers and social workers.
As such an exposed group, they believe that the frequency of CRP is higher. In fact, the median between them is 10 tests. Despite the high exposure, the reinfection rate is still 1.2%, slightly lower than twice that of the general population. And the estimated protection rate is 81.1%.
In addition, in the reanalysis, they placed all Danes who had undergone two or more tests (2.5 million people) in the same package, without distinguishing between the first wave and the second wave. In summer, infected people will also enter here. The percentage of re-infection at least three months after the first infection was 0.48%. Regarding the estimated protection, although it is still less than half of the elderly, it is close to 80%.
The co-author of the study and the author of the International Space Station, Dr. Daniela Michlmayr (Daniela Michlmayr), said that they did not observe any evidence that “the protection against reinfection declined within six months after receiving Covid. anything”.
It also mentioned that viruses related to current viruses (such as those that caused SARS and MERS epidemics in the first decade of this century) have immunity for 2 to 3 years.
He warned: “Continuous monitoring of Covid is needed to understand its long-term impact on the patient’s chance of re-infection.”
At the same time, ISGlobal epidemiologist Quique Bassat believes these percentages are high.
“We started with the idea that those infected are unlikely to be infected again.”
But he believes that many of these cases may actually be due to “persistent PCR positive, you are not infectious, or your viral load is low, but you are still testing positive.”
In fact, in a work they did in Barcelona last summer, they saw a clear “positive cohort”, and the infected people tested positive two or three months after being infected.
Professors Rosemary Bolton and Daniel Altman of Imperial College London commented on the research in the same issue of The Lancet. They concluded: “All these data confirm that if necessary, people hope to be able to SARS-CoV-2 may not be enough due to natural infection. The lasting solution is a universal vaccination plan with highly effective vaccines.”