JMIR Publications

ABSTRACT

Background:

As the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) attenuates and antibodies from the coronavirus disease 2019 (COVID-19) vaccine decline, long-term attention should be paid to the durability of primary-booster administration and the preventive effect of the second- or multiple-booster doses of COVID-19 vaccine.

Objective:

To determine the effect and durability of primary-booster administration (the third dose) and prospectively assess the immunogenicity and real-world protective effect of secondary booster heterologous immunization (the fourth dose) against SARS-CoV-2.

Methods:

A bidirectional cohort was established in Guizhou Province, China. Eligible participants who had received the primary-booster doses were enrolled for blood sample collection and administration of the second-booster dose. A retrospective cohort for the time of administration was constructed to evaluate antibody attenuation 6-12 months after the primary-booster dose, while a prospective cohort was constructed for four months after the second booster. One month after administration, blood samples were collected to determine the antibody levels produced by booster inoculation. At month 4 after the second booster, the individuals were contacted via telephone to collect information including COVID-19 infection and long COVID symptoms.

Results:

Between September 21, 2022 and January 30, 2023, 327 participants were included in the final statistical analysis plan. The retrospective cohort revealed that approximately 6-12 months after receiving the primary booster, the geometric mean titers (GMT) of IgG slowly declined with time, while the IgA antibody level remained almost constant (7.9). The prospective cohort showed that at 28 days after receiving the second booster, the antibody levels of individuals with different sociodemographic characteristics were significantly improved. Higher levels of post-immunization IgG and IgA antibodies were associated with better protection against COVID-19 infection and a lower cumulative risk for vaccine recipients. Regarding the protection of antibody levels against long COVID symptoms, the geometric mean increase (GMI) levels of the IgG antibodies had a protective effect on brain fog and sleep quality, while IgA had a protective effect on shortness of breath, brain fog, impaired coordination, and physical pain.

Conclusions:

The IgG and IgA antibodies produced by the second-booster dose of COVID-19 vaccines can protect against SARS-CoV-2 infection and may alleviate some long COVID symptoms. Further data and studies on secondary booster administration are required to confirm these conclusions.