Infectiousness peaks in first five days of COVID-19 symptoms, research suggests

Buenos Aires Starts A Slow Reopening Process Amid Coronavirus Pandemic Peak

The Oxford study enrolled more than 12,000 healthcare workers of which 11,000 tested negative for Covid-19 antibodies.

The WHO said it is working with 50 countries where studies on antibody responses in different groups, such as in the general population or among healthcare workers, were taking place.

Individuals infected with coronavirus are unlikely to catch the illness again for at least six months, researchers at the University of Oxford said Friday.

"Our study demonstrates that it is critical to recognize that older adults with COVID-19 may present with delirium as the primary or sole symptom", the study says.

The authors said that development of B cell memory to SARS-CoV-2 appeared to be robust and was likely long-lasting. "B cell memory to some other infections has been observed to be long-lived, including 60+ years after smallpox vaccination or 90+ years after infection with influenza, another respiratory virus like SARS-CoV-2", reads the study.

An additional 76 workers who had not been infected before and didn't have the antibodies for COVID-19 tested positive, but were asymptomatic.

Although the research, published online in pre-print server bioRxiv, has not been peer-reviewed nor published in a scientific journal, the New York Times refers to it as "the most comprehensive and long-ranging study of immune memory to the coronavirus to date".

However, in humans, if this passive transfer of neutralizing antibodies provided after the infection had already started, the infection severity could not be significantly controlled.

According to the study, the immunological memory for SARS-CoV-2 could last as long as six months after an infection.

This means that the T cells within the infected person play a significant role in protecting against secondary infection rather than the antibodies alone, write the researchers.

Presently, most diagnostic methods involve sampling nasal fluids, saliva or blood, followed by nucleic acid-based tests for detecting active infections or blood-based serological detection for past infections.

Part of the reason researchers studied all three diseases was to determine why COVID-19 has spread more rapidly than the earlier diseases.

In recent months, reports of waning antibody levels have created worry that immunity to the coronavirus may disappear in a few months, leaving people vulnerable to the virus again.

The researchers note that numerous hospitalized patients included in the studies they reviewed received treatments that may have affected the course of their infection.

All 100 people had high Covid-specific T cells six months later, mirroring the findings from the latest antibody study, but the antibody number in this cohort had dropped below detectable levels.