An ISGlobal study followed 247 Catalan healthcare workers from the start of the pandemic until November 2021, prior to the arrival of omicron, the most infectious variant to date
The unvaccinated persons who have passed covid-19 can maintain antibodies at least 20 months after the disease. This is suggested by a study conducted, before the arrival of omicron (the most infectious variant of all), in a cohort of unvaccinated health care personnel and recently published in the journal ‘BMC Medicine’, led by the Barcelona Institute for Global Health (ISGlobal), a center promoted by La Caixa and the Institut Catalá de la Salut (ICS).
The obesity, the age and being smoker are associated with a lower antibody response. In fact, another study published in September by ISGlobal claimed that the 36% of people in between 43 and 72 years old that were infected with covid-19 a year ago and that were not vaccinated already had no detectable antibodies, and that this occurred mostly in those over 60 years of age and smokers.
Almost 35% of the world’s population remains without receiving even a single dose of covid-19 vaccine, so that their immunity to the virus depends exclusively on infection. Therefore, knowing how long the immune response lasts after infection and its effectiveness. is are KEY ELEMENTS to guide decisions on how to control this and future coronavirus pandemics. The new study now from ISGlobal advocates that the hybrid immunity (vaccination plus infection) is the most protective.
The ISGlobal-led study was conducted in a cohort of Catalan health care workers from between 40 and 70 years of age. One in three people no longer had detectable antibodies one year after infection. “The cohort of health care personnel described here includes younger and more exposed people. to the virus, who suffered a symptomatic infectionand in which we have been able to take regular samples over almost two years”, says the ISGlobal researcher. Carlota Dobaño.
The research team evaluated the persistence of antibodies in. 247 persons with symptomatic infection and not yet vaccinated, taken at eight different times. between summer 2020 and November 2021. The results show a gradual decline and considerable drop in antibody levels, but more than 90% of participants still had antibodies at all times during the study. Even in the 23 individuals who had not yet been vaccinated in November 2021, the seropositivity was maintained at 95%.
Only the following were observed eight reinfections during the follow-up period, which suggests that the immunity is robust and durable even against new variants. such as alpha and delta. The study, however, was performed before the advent of the omicron variant.
The analysis of samples taken just before the onset of vaccination confirms what was observed in previous studies: the age and smoking are associated with lower antibody levelswhile the hospitalization and certain symptoms (fever, loss of taste and smell) are associated with higher levels. “This would also explain why in this study we are seeing such long-lasting seropositivity, as all infections recorded in healthcare personnel were symptomatic,” Dobaño points out.
The results suggest that maintaining detectable antibody levels confers. protection against reinfection even in the absence of vaccination. However, the research team points out, this study was conducted prior to the advent of omicron, and that the previously infected people also benefit from vaccination.since the hybrid immunity best protects against infection and disease.