Analysis of immunization, adverse events, and efficacy of a fourth dose of BNT162b2 vaccine
Authors: Romero-Ibarguengoitia Maria Elena , González-Cantú Arnulfo , Rivera-Salinas Diego , Hernández-Ruíz Yodira Guadalupe , Armendariz-Vázquez Ana Gabriela , Barco-Flores Irene Antonieta , González-Facio Rosalinda , Ángel Sanz-Sánchez Miguel 
Published: April 2022

AbstractImportanceScarce information exists concerning the seroconversion and adverse events after immunization (AEFI) of the fourth dose of a SARS-COV-2 vaccine.ObjectiveCorrelate the magnitude of the antibody response to vaccination with previous clinical conditions and AEFI of the fourth dose of BNT162b2 mRNA.DesignObservational study where SARS-CoV-2 spike 1-2 IgG antibodies IgG titers were measured 21-28 days after the exposition of the first, and second dose, three months after the second dose, 1-7 days after the third dose, before the fourth dose, and 21-28 days after the fourth dose of BNT162b2 mRNA.SettingThe study was conducted on healthcare workers of a private hospital in Northern Mexico.ParticipantsInclusion criteria were healthcare workers of both genders, any age, who planned to conclude the immunization regimen. The exclusion criteria were previously given any SARS-CoV-2 vaccine prior to study entry.InterventionSubjects were exposed to four doses of the BNT162b2 mRNA vaccine.Main Outcome and Measures:The anti-S1 and anti-S2 IgG antibodies against SARS-CoV-2 in plasma samples were measured with chemiluminescence immunoassay developed by DiaSorin.ResultsWe recruited 112 subjects [43 (SD 9) years old, 74% women].After the first dose, subjects had a median (IQR) AU/ml IgG of 122(1904), with an increase to 1875 (2095) after the second dose, 3020 (2330) after the third dose, and 4230 (3393) after 21-28 of a fourth dose (p<0.01). The number (%) of any AEFI between doses was 90 (80.4), 89(79), 65(58), 69 (61.5), after first, second, third, and fourth, respectively, p<0.001. After the fourth dose, the most frequent AEFI was pain at the injection site (87%). Fever was slightly more frequent after the third and fourth doses, 9 (13.8) and 8 (11.4%) cases, respectively, and adenopathy was more frequent after the fourth dose [in11(15.7%) cases]. There was a correlation between AEFI in the fourth dose with gender and antibody levels (p<0.05). The highest proportion of AEFI was considered mild after the fourth dose. During the Omicron outbreak, 6 (5.3%) had mild SARS-CoV-2 during 8-28 days of the fourth dose.Conclusions and RelevanceThe fourth dose of BNT162b2mRNA increases S1/S2 IgG 33.6 times with mild adverse events.Registration numberNCT05228912Key pointsQuestionWhat is the magnitude of antibody response to vaccination and adverse events after immunization (AEFI) of a fourth dose of BNT162b2 mRNA?FindingsThis cohort included 112 healthcare workers. We measured S1/S2 IgG vs. SARS-CoV-2 after the first, second, third and fourth dose. Compared to the first dose, antibodies increased 33.6 times the antibody levels after the fourth dose. We found minimal to moderate adverse events. The change in antibodies correlated with AEFI. During the Omicron outbreak 6 (5.3%) had mild SARS-CoV-2.MeaningA fourth dose of BNT162b2mRNA increases S1/S2 IgG with mild to moderate adverse events.