BEIJING (Reuters) - Levels of an antibody found in recovered COVID-19 patients fell sharply in 2-3 months after infection for both symptomatic and asymptomatic patients, according to a Chinese study, raising questions about the length of any immunity against the novel coronavirus.
FILE PHOTO: A computer image created by Nexu Science Communication together with Trinity College in Dublin, shows a model structurally representative of a betacoronavirus which is the type of virus linked to COVID-19, better known as the coronavirus linked to the Wuhan outbreak, shared with Reuters on February 18, 2020. NEXU Science Communication/via REUTERS
The research, published in Nature Medicine on June 18, highlights the risks of using COVID-19 ‘immunity passports’ and supports the prolonged use of public health interventions such as social distancing and isolating high-risk groups, researchers said.
Health authorities in some countries such as Germany are debating the ethics and practicalities of allowing people who test positive for antibodies to move more freely than others who don’t.
The research, which studied 37 symptomatic patients and 37 asymptomatic patients, found that of those who tested positive for the presence of the IgG antibody, one of the main types of antibodies induced after infection, over 90% showed sharp declines in 2-3 months.
The median percentage decrease was more than 70% for both symptomatic and asymptomatic patients.
For neutralising serum antibodies, the median percentage of decrease for symptomatic individuals was 11.7%, while for asymptomatic individuals it was 8.3%.
The study was conducted by researchers at Chongqing Medical University, a branch of the Chinese Center for Disease Control and Prevention and other institutes.
Jin Dong-Yan, a virology professor at the University of Hong Kong who was not part of the research group, said the study does not negate the possibility that other parts of the immune system could offer protection.
Some cells memorize how to cope with a virus when first infected and can muster effective protection if there is a second round of infection, he said. Scientists are still investigating whether this mechanism works for the new coronavirus.
“The finding in this paper doesn’t mean the sky is falling,” he said, also noting that number of patients studied was small.
Na maioria das pessoas que tiveram , após oito semanas o nível de anticorpos no corpo diminui. Pesquisadores da  publicaram na revista '''' um estudo com 37 pacientes assintomáticos da província chinesa de Wanzhou.

Eles compararam a resposta de seus anticorpos ao de 37 pessoas que apresentavam sintomas e descobriram que pacientes sem sintomas apresentavam uma resposta imune mais fraca do que aqueles que apresentavam sintomas.

Os cientistas descobriram que entre aqueles que testaram positivo para a presença de um , um dos principais tipos de anticorpos, mais de 90% experimentaram uma queda acentuada nos anticorpos após 2–3 meses.

Durante as oito semanas de observação, os anticorpos diminuíram em 81% dos pacientes assintomáticos e em 62% dos portadores com sintomas. O número de anticorpos diminuiu para um nível indetectável em 40% dos casos assintomáticos, em comparação com 12,9% nos casos sintomáticos.

A partir dos resultados do estudo, conclui-se que as reinfecções são apenas uma questão de tempo, não sendo produzida imunidade estável ao vírus, especialmente em pacientes assintomáticos. E a imunidade temporária não dura mais que 2–3 meses.

No mundo, o número de casos detectados de coronavírus ultrapassou 9 milhões, mais de 472 mil pessoas morreram, mais de 4,5 milhões foram curadas.