Humoral Immune Responses following COVID-19 Vaccinations among Adults in Tanzania
Muhammad Bakari,
Said Aboud,
Mabula Kasubi,
Bruno P. Mmbando,
Nyanda Elias Ntinginya,
Aifello Sichalwe,
Omary S. Ubuguyu,
Alex Magesa,
Nancy Ladislaus Rutananukwa,
Helmut Nyawale,
Abisai Kisinda,
Medard Beyanga,
Pius G. Horumpende,
Paulo S. Mhame,
Liggle M. Vumilia,
Lucy S. Mziray,
Reuben Mkala,
Elichilia Shao,
Abel Makubi,
Stephen E. Mshana,
Rogath Kishimba
Affiliations
Muhammad Bakari
School of Medicine, Muhimbili University of Health and Allied Sciences (MUHAS), Dar es Salaam P.O. Box 65001, Tanzania
Said Aboud
School of Medicine, Muhimbili University of Health and Allied Sciences (MUHAS), Dar es Salaam P.O. Box 65001, Tanzania
Mabula Kasubi
Muhimbili National Hospital (MNH), Dar es Salaam P.O. Box 65000, Tanzania
Bruno P. Mmbando
National Institute for Medical Research (NIMR), Dar es Salaam P.O. Box 9653, Tanzania
Nyanda Elias Ntinginya
National Institute for Medical Research (NIMR), Dar es Salaam P.O. Box 9653, Tanzania
Aifello Sichalwe
Ministry of Health (MoH), Dodoma P.O. Box 743, Tanzania
Omary S. Ubuguyu
Ministry of Health (MoH), Dodoma P.O. Box 743, Tanzania
Alex Magesa
Ministry of Health (MoH), Dodoma P.O. Box 743, Tanzania
Nancy Ladislaus Rutananukwa
National Institute for Medical Research (NIMR), Dar es Salaam P.O. Box 9653, Tanzania
Helmut Nyawale
Department of Microbiology and Immunology, Weill Bugando School of Medicine, Catholic University of Health and Allied Sciences (CUHAS), Mwanza P.O. Box 1464, Tanzania
Abisai Kisinda
National Institute for Medical Research (NIMR), Dar es Salaam P.O. Box 9653, Tanzania
Medard Beyanga
Ministry of Health (MoH), Dodoma P.O. Box 743, Tanzania
Pius G. Horumpende
Ministry of Health (MoH), Dodoma P.O. Box 743, Tanzania
Paulo S. Mhame
Ministry of Health (MoH), Dodoma P.O. Box 743, Tanzania
Liggle M. Vumilia
Ministry of Health (MoH), Dodoma P.O. Box 743, Tanzania
Lucy S. Mziray
Ministry of Health (MoH), Dodoma P.O. Box 743, Tanzania
Reuben Mkala
Benjamin Mkapa Hospital (BMH), Dodoma P.O. Box 11088, Tanzania
Elichilia Shao
Kilimanjaro Christian Medical Centre (KCMC), Moshi P.O. Box 3010, Tanzania
Abel Makubi
Ministry of Health (MoH), Dodoma P.O. Box 743, Tanzania
Stephen E. Mshana
Department of Microbiology and Immunology, Weill Bugando School of Medicine, Catholic University of Health and Allied Sciences (CUHAS), Mwanza P.O. Box 1464, Tanzania
Rogath Kishimba
Ministry of Health (MoH), Dodoma P.O. Box 743, Tanzania
COVID-19 vaccination remains to be the most important intervention in the fight against the pandemic. The immunity among the vaccinated population and its durability can significantly vary due to various factors. This study investigated the humoral immune responses among individuals who received any of the COVID-19 vaccines approved for use in Tanzania. A total of 1048 randomly selected adults who received COVID-19 vaccines at different time points were enrolled and humoral immune responses (IR) were tested at baseline and three months later (960, 91.6%). The level of SARS-CoV-2 anti-spike/receptor binding domain (RBD) IgG, anti-nucleocapsid IgG, and IgM antibodies were determined using a commercially available chemiluminescent microparticle immunoassay. Descriptive data analysis was performed using STATA version 18 and R. At baseline, serum IgG against anti-spike/RBD was detected in 1010/1048 (96.4%) participants (95%CI: 94.9–97.5) and 98.3% (95%CI: 97.3–99) three months later. The IgG against the SARS-CoV-2 nucleocapsid proteins were detected in 40.8% and 45.3% of participants at baseline and follow-up, respectively. The proportion of seroconverters following vaccination and mean titers of anti-spike/RBD antibodies were significantly more among those who had past SARS-CoV-2 infection than in those with no evidence of past infection, (p < 0.001). Only 0.5% of those who had detectable anti-spike/RBD antibodies at baseline were negative after three months of follow-up and 1.5% had breakthrough infections. The majority of participants (99.5%) had detectable anti-spike/RBD antibodies beyond 6 months post-vaccination. The proportion of Tanzanians who mounted humoral IR following COVID-19 vaccination was very high. Seroconversions, as well as the mean titers and durability of humoral IR, were significantly enhanced by exposure to natural SARS-CoV-2 infection. In view of the limited availability of COVID-19 vaccines as well as challenges to completing subsequent doses, booster doses could only be suggested to high-risk groups.
