Had Covid in the past nine months? Your body has a chance against Delta

Whether you have had severe Covid-19 or an infection with no symptoms, you can expect to have antibodies to the virus nine months later, a new study shows.

At the start of the pandemic in February and March last year, researchers tested more than 85% of the 3,000 residents of the Italian town Vo’ for Covid-19. In May and in November 2020, they tested them again for antibodies against coronavirus.

They found that 98.8% of the people infected in February or March had detectable antibodies in November, in the study published in the journal Nature Communications on Monday.

When they did mass swab testing, the teams, from the University of Padova, Italy, and Imperial College, UK, recorded that 3.5% of the Vo’ population had been exposed to the virus but a “large fraction” had had asymptomatic infections and were unaware of this.

The researchers also found that antibody levels increased in some residents who were potentially reinfected, with the virus boosting their immune response.

“We found no evidence that antibody levels differ significantly between symptomatic and asymptomatic infections, suggesting that the strength of the immune response does not depend on the symptoms and the severity of the infection,” said the lead author Dr Ilaria Dorigatti, from the MRC Centre for Global Infectious Disease Analysis and the Abdul Latif Jameel Institute for Disease and Emergency Analytics at Imperial College London.

Roughly one in four people who tested positive with Sars-CoV-2 would infect family members or people in the household, they reported.

The strength of the immune response does not depend on the symptoms and the severity of the infection.

But the Delta variant, now dominant in SA and rising globally, has a much higher risk of infecting people sharing a home, being 30% to 60% more transmissible.

Prof Enrico Lavezzo, from Padova University, said the antibody levels had dropped nine months after the outbreak.

“At the follow-up ... we found that antibodies were less abundant, so we need to continue to monitor antibody persistence for longer time spans,” he said.

The researchers tracked the antibody levels of Vo’ residents using three tests (assays) “to detect the different types of antibodies that respond to different parts of the virus”.

Dorigatti said antibody levels varied depending on the test used. “This means caution is needed when comparing estimates of infection levels in a population obtained in different parts of the world with different tests and at different times.”

The teams concluded: “Physical distancing, as well as limiting the number of contacts and mask wearing, continue to be important to reduce the risk of transmitting the disease, even in highly vaccinated populations ... it is of fundamental importance to continue administering first and second vaccine doses.”

By Tuesday morning, 5.3 million Covid-19 vaccine doses had gone into the arms of South Africans, though only 1.79 million of South Africans were fully vaccinated.

Until vaccination is more widespread in SA, most people will have to rely on the antibodies they have developed from prior infections to reduce their Covid-19 risk.

Neutralising antibodies are reported to be four to six times less effective against the Delta variant than other variants of Sars-CoV-2.

But in some areas, for example Khayelitsha in Cape Town, antibodies could be a buffer against Covid-19 accelerating. Khayelitsha had the highest rates of new infections per day of the subdistricts in Cape Town in the first wave, at 169 new cases per day (a seven-day moving average). Now it has the lowest infection rate, at 26 new cases per day reported on Monday — even as the third wave rises in the Western Cape.