The contributions of vaccination and natural infection to the production of neutralizing antibodies against the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) prototype strain and variants.

OBJECTIVES: To evaluate the neutralizing antibody (NAbs) levels against the SARS-CoV-2 Omicron variants BF.7, BQ.1, BQ.1.1, XBB.1, and XBB.1.5 after vaccination and natural infection.

METHODS: The NAbs against the different viral strains of 490 SARS-CoV-2 infected and 187 uninfected individuals in Beijing COVID-19 outbreak during December 2022 to January 2023 were analyzed.

RESULTS: In uninfected individuals, limited levels of NAbs were produced against both the prototype and variant strains after two doses vaccine, but significantly increased after three or four doses vaccine. The infected individuals had high NAbs levels against the BF.7, BQ.1, and BQ.1.1 variants and moderate NAbs levels against the XBB.1 and XBB.1.5 variants. The highest NAbs levels were observed after two inoculation doses. The third and fourth doses vaccine did not result in a significant increase the NAbs levels. After the last dose of vaccination, the NAbs levels peaked at 12 months for the prototype and BF.7 and between 6 to 12 months for the BQ.1, BQ.1.1, XBB.1, and XBB.1.5 variants.

CONCLUSION: The immune response decreases as the virus mutates. If booster vaccination is considered necessary, it is suggested for at least 6 months after infection.