Coronavirus antibodies may last only two to three months after a person becomes infected with Covid-19, according to a new study published Thursday in Nature Medicine.
Researchers examined 37 asymptomatic people, those who never developed symptoms, in the Wanzhou District of China. They compared their antibody response to that of 37 people with symptoms. The researchers found people without symptoms had a weaker antibody response than those with symptoms.
Within eight weeks, 81% of the asymptomatic people saw a reduction in neutralizing antibodies, compared with 62% of symptomatic patients. Additionally, antibodies fell to undetectable levels in 40% of asymptomatic people, compared with 12.9% of symptomatic people, according to the study's findings.
Though the study is small, the researchers noted the findings may spur some world leaders to rethink issuing so-called "immunity passports." Some countries have considered issuing passports or risk-free certificates to people who have antibodies against Covid-19, enabling them to travel or return to work assuming that they are protected against reinfection.
Scientists say they are still learning about key aspects of the virus, including how immune systems respond once a person is exposed. The answers, they say, may have large implications for vaccine development, including how quickly it can be deployed to the public.
One critical question among scientists is whether antibodies produced in response to Covid-19 offer protection against getting infected again. Additionally, scientists are still unsure of how long immunity lasts if antibodies do provide protection.
In general, antibodies that help the body fight off infections are produced in response to invading foreign particles or antigens. Vaccines work by inducing the immune system to produce these molecules. Health officials have said there is not enough data to indicate that coronavirus antibodies ensure immunity against the virus.
Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said earlier this month that a vaccine may not provide long-term immunity if Covid-19 behaves like other coronaviruses.
"When you look at the history of coronaviruses, the common coronaviruses that cause the common cold, the reports in the literature are that the durability of immunity that's protective ranges from three to six months to almost always less than a year," he said during an interview on June 2 with JAMA Editor Howard Bauchner. "That's not a lot of durability and protection."
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.