COVID antibodies remain stable – and even increase – seven months after infection, according to the biggest study of its kind during the pandemic.

Researchers in Spain have discovered that pre-existing antibodies to common cold coronaviruses may be protective against COVID-19. The follow-up study among a group of healthcare workers was coordinated by the Barcelona Institute for Global Health (ISGlobal).

Scientists say it is crucial to better understand the dynamics and duration of immunity to SARS-CoV-2, the virus that causes COVID-19, to predict the pandemic’s evolution and develop effective strategies to combat its spread.

With that goal in mind, ISGlobal researcher Professor Carlota Dobaño and other scientists followed a group of healthcare workers from the beginning of the pandemic to evaluate the levels of antibodies against different SARS-CoV-2 antigens over time.

“This is the first study that evaluates antibodies to such a large panel of SARS-CoV-2 antibodies over 7 months,” says Prof Dobaño in a media release.

Can Other Coronavirus Antibodies Protect against COVID-19?

The researchers analyzed blood samples from 578 participants, taken at four different times between March and October 2020. They measured the level and type of antibodies to six different SARS-CoV-2 antigens as well as the presence of antibodies against the four other coronaviruses that cause common colds in humans.

The results, published in the journal Nature Communications, show that the majority of infections among healthcare workers occurred during the first pandemic wave. The percentage of participants with SARS-CoV-2 antibodies increased only slightly between March and October – from 13.5 percent to 16.4 percent.

Antibodies largely remained stable over time, confirming results from other recent studies. Additionally, the team did not note any reinfections among the group.

“Rather surprisingly, we even saw an increase of IgG anti-Spike antibodies in 75% of the participants from month five onwards, without any evidence of re-exposure to the virus,” says study senior co-author and assistant research professor Gemma Moncunill.

Regarding antibodies against human cold coronaviruses (HCoV), the results suggest that they could confer cross-protection against COVID-19 infection or other diseases. People infected by SARS-CoV-2 had lower levels of HCoV antibodies. Asymptomatic individuals had higher levels of anti-HCoV antibodies than those with symptomatic infections.

“Although cross-protection by pre-existing immunity to common cold coronaviruses remains to be confirmed, this could help explain the big differences in susceptibility to the disease within the population,” Prof. Dobaño concludes.