Filenews 26 July 2021
Screening of citizens of an entire city in Italy has shown that antibody levels remain high up to nine months after SARS-CoV-2 infection, be they patients with symptoms or asymptomatics, according to a new scientific study published in Nature Communications.
Researchers from the University of Padva and Imperial College London examined more than 85% of the 3,000 inhabitants of the Vo community of the province of Padva in February and March 2020 for coronavirus and again in May and November of the same year for antibodies against the virus.
The team found that 98.8% of people infected in the spring had detectable levels of antibodies in November, which made no difference between those who suffered from COVID-19 symptoms and those who were asymptomatic.
Antibody levels were monitored through three "tests"- tests that identify different types of antibodies that respond to different parts of the virus. The results showed that while all types of antibodies showed some decline between May and November, the rate of attenuation was different depending on the control test.
The scientific team also found cases where antibody levels were increasing in some people, indicating possible re-infections from the virus, which provided some boost to the immune system.
"We found no evidence that levels of antibodies between symptomatic and asymptomatic differ significantly, indicating that the strength of the immune response does not depend on the symptoms and severity of the infection. However, our study shows that levels of antibodies vary - and sometimes significantly - depending on the test used. This means that caution is needed when comparing estimates of infection levels in different populations, with different diagnostic tests and at different times," explains lead author from J-IDEA, Dr. Ilaria Dorigatti.
In turn, the professor at the University of Padova, Dr . Enrico Lavezzo points out: "The May audit showed that 3.5% of the Vo population had been exposed to the virus, although not everyone was aware of their exposure, given the large portion of asymptomatic infections. However, during subsequent monitoring, which took place almost nine months after the outbreak of the pandemic, we found that antibodies were less abundant, so we must continue to monitor the presence of antibodies for longer periods of time."
The scientists also investigated the infection status of members of each family to assess how likely an infected member is to transmit the infection within the household. Their modelling, therefore, indicates that there was a 1 in 4 chance that an infected person would transmit the infection to a family member and that the greatest transmission (79%) of the infection was caused by 20% of infections.
The findings confirm that there are large differences in the number of second cases produced by infected people, with the majority of infections producing no further infections and the minority producing a large number of new infections.
Finally, the large differences in the way an infected person can infect others indicate that behavioural factors are the key to controlling the epidemic and that social distance as well as the restriction of social contacts and the use of masks continue to be important in reducing the risk of transmission of the disease, even in populations with high vaccination coverage.
The data used by the researchers also allowed them to separate the impact of the various control measures, demonstrating that in the absence of quarantine and short lockdown, individual contact tracing would not be enough to suppress the epidemic.
