People who have had COVID-19 infection could have longer-term protection against the virus compared to those who have been vaccinated and not had the disease, an Israeli study has found.
Research, to be presented at the European Congress of Clinical Microbiology & Infectious Diseases (ECCMID) in Lisbon in April, shows that, although SARS-CoV-2 antibodies fall in both previously infected and vaccinated patients, the performance of antibodies improves only after previous infection and not vaccination.
It is believed this difference could explain why previously infected patients seem to be better protected against a new infection than those who have only been vaccinated.
Dr Carmit Cohen, of the Sheba Medical Centre, Ramat Gan, Israel, and colleagues, also found that obese people who were previously infected had a higher and more sustained immune response than overweight and normal weight range patients.
The study analysed the antibody-induced immune response in unvaccinated people who had recovered from COVID-19 for up to a year and compared it with those who had had no previous infection and had received two doses of the Pfizer vaccine over eight months.
The study recruited previously infected-unvaccinated and double-vaccinated-never infected individuals from 25 March 2020 to 25 November 2020.
The researchers followed-up of 130 patients who had had PCR-confirmed COVID-19 and had not vaccinated and who remained unvaccinated during the study.
None was reinfected across the study period.
Data were collected on acute and long-term symptoms and the research team compared anti-spike protein IgG and neutralising antibodies of the 130 recovered patients to 402 individuals who were matched to age and body mass index (BMI) and who were double-vaccinated with the Pfizer vaccine but who had never had COVID-19.
The double-vaccinated participants remained uninfected across the study period. However, in the second quarter of 2021, evidence emerged that double vaccinated healthcare workers who had never had COVID-19 experienced breakthrough infections at about six months after their second dose.
The study explored why this would happen when previously infected individuals that had not been vaccinated were not being reinfected.
The researchers set up sub-cohorts of 16 people who had recovered from COVID-19 and 22 never-infected individuals who had been double vaccinated to compare the avidity index. Questionnaires covering symptoms, including Long COVID, were given to those who had recovered from the virus.
They found the number of antibodies a month after vaccination was higher than those in the COVID-19 recovered patients, but these numbers declined more steeply in the vaccinated group.
The avidity index was higher in vaccinated individuals than in recovered patients initially, but avidity did not significantly change in vaccinated individuals up to six months avidity, while it increased gradually in recovered patients and potentially protected them from reinfection.
Against expectations, the level of antibodies in recovered patients with a body mass index of 30 or higher was higher at all times when compared with those with a BMI under 30.
This, suggests the team, seems to show that obese individuals who had been previously infected were better protected against future infection than those who were overweight or normal weight and had been previously infected.
Out of all recovered patients, 42 (36%) experienced Long COVID symptoms, of which 5% were mental health, 9% neurological, 5% cardiovascular, and 31% respiratory manifestations.
“While the number of antibodies decreases with time in both COVID-19 recovered (but never vaccinated) patients and vaccinated (but never infected) individuals, the quality of antibodies increases following infection but not after vaccination,” say the authors.
“People with obesity have a significantly higher and sustained antibody-induced immune response following infection. These results provide specific characteristics of the immune response that may explain the differential protection against COVID-19 in previously infected compared with only-vaccinated individuals.”
The research has not yet been submitted for publication.
The team is now following a cohort of people who recovered from the delta variant as well as a separate cohort who recovered from the omicron variant, to examine both the humoral and innate immune responses.
Dr Cohen adds: “With the omicron variant, vaccinated individuals are better protected from severe disease, yet the fourth vaccine dose, now given to many people over 60 years old and those who are immunocompromised, does not appear to be protective against infection with the omicron variant.
“I think that the most interesting people to follow up now are those who have recovered from the earlier variants and have then been re-infected by, and recovered from, infection with the omicron variant. Hypothetically, these individuals should have very high antibody performance against most variants.”
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