Antibody levels in recovered COVID-19 patients may decline within three months

Immunity to coronavirus may last for as little as six weeks, new research from China suggests.  

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 the Chinese study.

Although the study was small, its outcome raises questions about the length of any immunity against the novel coronavirus.

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, the researchers from Chongqing Medical University said.

Whether survivors were asymptomatic (left in each graph) or symptomatic (right in aech), antibody levels began to decline within two to three months of infection, a new study found

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 percent showed sharp declines in 2-3 months.

The median percentage decrease was more than 70 percent for both symptomatic and asymptomatic patients.

For neutralizing serum antibodies, the median percentage of decrease for symptomatic individuals was 11.7 percent while for asymptomatic individuals it was 8.3 percent. 

Scientists had hoped that antibodies for SARS-CoV-2 would have similar staying power to immunity seen in people infected with its closes cousins, SARS and MERS. 

Antibodies to each last at least a year, and the levels of SARS antibodies remain stable for up to two years after infection before declining. 

That did not prove to be the case in the new study. 

Most of the COVID-19 patients had declining levels of antibodies within a couple of months. 

Four out of eight patients that the researchers followed through their ‘convalescent’ stage (meaning they had recovered, but still might have signs of the virus inside their bodies) lost most of their antibody protection within six to seven weeks. 

States across the US, as well as other nations, are beginning to reopen for business with a vaccine likely still months away. 

The short-term protection that the new study suggests is offered by coronavirus antibodies means that even someone who contracted coronavirus in March may now already be vulnerable to re-infection.  

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.

Urging against alarm, he said: ‘The finding in this paper doesn’t mean the sky is falling,’ and noted that number of patients studied was small.