RIO DE JANEIRO, BRAZIL – The immune systems of the vast majority of people who have been infected with the virus continue to carry antibodies to the virus for at least 12 months.
This is according to a respected peer-reviewed study published Septenber 24 in the European Journal of Immunology.
Scientists from the Finnish Institute of Health and Welfare examined the presence of antibodies in 1,292 people eight months after infection. They found that 96 percent of the subjects still carried neutralizing antibodies, and 66 percent still carried a type of antibody called IgG nucleoprotein.
The researchers then examined antibody levels one year after infection by randomly selecting 367 people from the original cohort who had not yet been vaccinated. Eighty-nine percent of the subjects still carried neutralizing antibodies, and 36 percent still carried IgG antibodies.
Antibody levels were higher in subjects who had experienced severe Covid-19 disease. Compared with individuals with mild disease, these individuals had two to seven times more antibodies for at least 13 months after infection.
“Studies of individuals who have recovered from infection are critical to determining how long the antibodies persist after infection and whether these antibodies protect against re-infection,” the researchers write.
Despite the long-lasting protection against the original viral strain, the study found that neutralization efficiency against alpha, beta and delta variants decreased over time.
The reduction in efficiency was “significantly lower” for the beta variant and “only slightly lower” for the alpha variant.
For the delta variant, the predominant strain in the United States, the study found that 80 percent of subjects still had immune protection 12 months after infection.
A study published in May in the journal Nature Medicine found that the level of neutralizing antibodies in a person is highly predictive of immune protection against severe infections and diseases caused by the virus.
Previous studies have shown that antibodies are present six to 12 months after infection.
Despite the robust and long-lasting protection after infection, vaccination requirements against the virus in the United States do not provide exemptions based on acquired immunity.