Objective: This study aims to report the incidence and characteristics of breakthrough infections among medical students in the first Philippine private medical school that resumed limited face-to-face classes and clinical rotations from July to December 2021. Methods: This is a descriptive study using secondary worksheet from multiple-source records review of breakthrough infections among medical students from July to December 2021. Results: Among the 837 vaccinated medical students, 23 (2.7%) experienced COVID-19 breakthrough infections. Of these, 9 were male and 14 were female. Four were asymptomatic and 19 were symptomatic. Of the 19 symptomatic, 18 had mild and 1 had severe disease. Mild infections presented with upper respiratory tract symptoms. Duration of symptoms ranged from 4 to 27 days with an average of 10 days. Timing of breakthrough infections ranged from 35 to 212 days after the second dose of COVID-19 vaccine with a mean of 86 days. Contact with confirmed cases was reported in 14 of 23 cases, 13 were from household members and none within the SLICE and CLARO programs. Conclusion Our study showed that even in the midst of the Delta surge, low breakthrough infection rate with mostly mildly symptomatic cases and no case transmissions within the SLICE and CLARO programs are possible with vaccination, regular health surveillance, and strict adherence to minimum health protocols.
Breakthrough Infections ; COVID-19 ; Philippines ; Students, Medical ; Vaccination

OBJECTIVE: To investigate whether Omicron BA.1 breakthrough infection after receiving the SARS-CoV-2 vaccine could create a strong immunity barrier. METHODS: Blood samples were collected at two different time points from 124 Omicron BA.1 breakthrough infected patients and 124 controls matched for age, gender, and vaccination profile. Live virus-neutralizing antibodies against five SARS-CoV-2 variants, including WT, Gamma, Beta, Delta, and Omicron BA.1, and T-lymphocyte lymphocyte counts in both groups were measured and statistically analyzed. RESULTS: The neutralizing antibody titers against five different variants of SARS-CoV-2 were significantly increased in the vaccinated population infected with the Omicron BA.1 variant at 3 months after infection, but mainly increased the antibody level against the WT strain, and the antibody against the Omicron strain was the lowest. The neutralizing antibody level decreased rapidly 6 months after infection. The T-lymphocyte cell counts of patients with mild and moderate disease recovered at 3 months and completely returned to the normal state at 6 months. CONCLUSION Omicron BA.1 breakthrough infection mainly evoked humoral immune memory in the original strain after vaccination and hardly produced neutralizing antibodies specific to Omicron BA.1. Neutralizing antibodies against the different strains declined rapidly and showed features similar to those of influenza. Thus, T-lymphocytes may play an important role in recovery.
Humans ; Antibodies, Neutralizing ; Prospective Studies ; SARS-CoV-2 ; Breakthrough Infections ; COVID-19 Vaccines ; COVID-19 ; T-Lymphocytes ; China/epidemiology* ; Antibodies, Viral