Long-lasting protection from omicron Ba.5

Luis Graca (group leader, Instituto de Medicina Molecular Joao Lobo Antunes, Lisbon), is leading a new study. Manuel Carmo Gomes (associate professor with aggregation, Faculty of Sciences of the University of Lisbon Ciencias ULisboa), are both part of the Direcao Geral de Saude, Technical Committee for Vaccination against COVID-19, (CTVC). This research was published in the scientific journal Lancet Infectious DiseasesThe protection provided by hybrid immunity against SARS-CoV-2 subvariant micron BA.5, which is obtained from the infected of people who have been vaccinated, can last at most eight months.

The results of this study follow those published by the researchers from the September issue. New England Journal of Medicine They found that the subvariant of SARS-CoV-2 which contained the first Omicron subvariants, which circulated in Portugal in January and February 2022 respectively, provided significant protection from infection. This variant is still the most prevalent in many other countries. The stability of hybrid immunity (the immunity that is conferred through the combination of infection and vaccination) was still unknown.

We had seen that the protection given by infection with the first subvariants of omicrons conferred protection to the BA.5 subvariant at about four times the level granted protection to vaccinated persons who weren’t infected. This shows the importance hybrid immunity as protection against future infections. We now show that the protection given by vaccines in combination with prior infections can be sustained for at least eighteen months. This is according to Luis Graca who was co-leader of this study.

The researchers also used the COVID-19 national case registry from September 2022 to complete the study. This is because all SARS-CoV-2 cases must be registered at the same time as mandatory isolation days to allow for sick leave. We used the COVID-19 national case registry to get information on all SARS-CoV-2 cases in Portugal’s population of over 12 year olds. This data, compiled from Portugal’s population, allows us to draw conclusions about hybrid immunity. By 2021 vaccination had reached 98%. Manuel Carmo Gomes was co-leader in the study. He explained that each virus type was identified based on the date and dominant variant.

Joao Malato (first author) explains the calculation made with the data. “With these data we calculated the relative danger of reinfection over the time in persons vaccinated against previous SARS-CoV-2 infections. This allowed us to determine the degree of protection against reinfection.” The protection level remains high eight months after the initial contact with virus.

Hybrid immunity provides protection of about 90% at first, decreasing to 70% after five months and stabilizing to around 65% by 8 months. This is in contrast to protection given to vaccinated people who were not infected with the virus. “These results demonstrate that the hybrid immunity conferred upon infection by previous subvariants SARS-CoV-2 is very stable,” Luis Graca explains about hybrid immunity’s protection.

The study demonstrated that the subvariants of SARS-CoV-2 viruses that caused COVID-19 can confer more protection than the vaccine alone. This protection has also been shown to be stable.

This information is provided by
Instituto de Medicina Molecular