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 Table of Contents  
Year : 2022  |  Volume : 29  |  Issue : 2  |  Page : 89-95

Adverse Events Following COVID-19 Vaccination in Rivers State, Nigeria: A Cross-Sectional Study

1 Department of Community Medicine, College of Medical Sciences, Rivers State University; Rivers State Primary Health Care Management Board, Port Harcourt, Nigeria
2 Rivers State Primary Health Care Management Board, Port Harcourt, Nigeria

Date of Submission12-Jan-2022
Date of Decision23-Feb-2022
Date of Acceptance28-Feb-2022
Date of Web Publication23-Apr-2022

Correspondence Address:
Clement Kevin Edet
Rivers State Primary Healthcare Management Board, Port Harcourt
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/npmj.npmj_11_22

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Context: Coronavirus disease (COVID-19) has led to over 2,589,638 deaths globally as of March 2021 and speedy discovery of vaccines. Nigeria started the phase one COVID-19 vaccination in March 2021 using the Oxford AstraZeneca vaccine. Reports of severe adverse events with the Oxford AstraZeneca vaccine resulted in its suspension in some countries necessitating the need to determine its safety. Aims: To assess the prevalence, types and severity of the adverse events following COVID-19 vaccination in Rivers State, Nigeria. Settings and Design: A cross-sectional study design was adopted. Subjects and Methods: Simple random sampling method was used to select a total of 428 adults from recipients of the first dose of COVID-19 vaccine within 28 days of vaccination. A questionnaire adapted from World Health Organisation was interviewer-administered through phone calls; responses were recorded on Kobo Toolbox. Statistical Analysis Used: Descriptive analysis of variables was done and the association between adverse events and age, allergy and medical history were determined. The level of statistical significance was predetermined at a P < 0.05. Results: In this study, 50.5% of respondents reported post-vaccination adverse events out of which 10 (4.6%) were severe (30% of the severe cases were life-threatening, 60% were hospitalised and 10% were placed on bed rest). The most common side effects were fever (73.0%), pain at the injection site (41.2%), fatigue (33.3%), body ache (17.5%) and headache (13.8%). No significant association was observed between the incidence of severe adverse events and participants with allergies or medical history. Conclusions: The adverse events associated with the COVID-19 vaccine were largely mild and resolved within a few days. Further research is required to classify adverse events into categories.

Keywords: Adverse events following immunisation, corona virus disease-2019, Nigeria, rivers state, vaccine

How to cite this article:
Harry AM, Edet CK, Ekanem NE, Kemdirim CJ, Uduak AE. Adverse Events Following COVID-19 Vaccination in Rivers State, Nigeria: A Cross-Sectional Study. Niger Postgrad Med J 2022;29:89-95

How to cite this URL:
Harry AM, Edet CK, Ekanem NE, Kemdirim CJ, Uduak AE. Adverse Events Following COVID-19 Vaccination in Rivers State, Nigeria: A Cross-Sectional Study. Niger Postgrad Med J [serial online] 2022 [cited 2023 Feb 7];29:89-95. Available from: https://www.npmj.org/text.asp?2022/29/2/89/343730

  Introduction Top

Coronavirus disease (COVID-19) is caused by an emerging coronavirus strain severe acute respiratory syndrome (SARS) coronavirus 2 that has not been previously identified in humans but is related to the viruses that cause SARS and the Middle East respiratory syndrome, both of which have been linked to zoonotic and person-to-person transmission.[1],[2],[3],[4] Coronavirus disease 2019 (COVID-19) started as an epidemic in mainland China, it was first reported in the city of Wuhan, Hubei Province on 8 December 2019.[5],[6],[7],[8],[9],[10],[11] Since then, the disease has been reported in more than 215 countries spread across the continents[12] and by 12 March 2020, the World Health Organisation (WHO) declared it a pandemic.[13] This pandemic wreaked havoc on the world's health-care systems,[14],[15] agricultural systems,[16],[17] life of higher education students,[18] mental health,[19] global economic crisis and a lot of other aspects of life globally.[4],[14],[20] More than 113 million active COVID-19 cases have been recorded by the WHO with over 2.5 million deaths as of 27 February 2021.[21]

On 27 February 2020, Nigeria recorded its first COVID-19 case (when an Italian citizen, who works in Nigeria, was diagnosed with the disease upon returning to Nigeria from a trip to Milan, Italy)[11],[22],[23],[24],[25],[26] while Rivers State recorded her first case on 26 March 2020.[17],[27],[28] Ever since then, the Nigeria Centre for Disease Control has been reporting an increase in the number of infected people daily.[29] Nigeria is one of 13 high-risk African nations for the transmission of COVID-19, according to the WHO.[30] According to the projections, Africa will bear the brunt of the COVID-19 pandemic if countries do not take strong anti-pandemic measures.[22] To this purpose, the Coronavirus Preparedness Group was established in Nigeria on 31 January 2020.[22],[31]

Exposure to SARS-CoV-2 can result in a range of clinical outcomes, varying from asymptomatic infection to severe acute respiratory distress and death.[4] The unique nature of the present coronavirus outbreak, as with previous outbreaks, meant that no definite medicine for its treatment existed.[20],[26] It has been managed clinically by first isolating the patient, administering supplemental oxygen therapy, empiric antibiotics treatment and closely monitoring the patient. COVID-19 has been treated with a variety of medicines. Hydroxychloroquine, azithromycin, chloroquine, ivermectin, cotrimoxazole, doxycycline, remdesivir, ulinastatin and colchicine are among these medications, although none has been unanimously recommended for COVID-19 treatment.[32]

From the beginning of the pandemic, scientists have been focusing on either repurposing existing medications or generating COVID-19 vaccines.[14],[33] The public and private sectors have joined together to develop and test potential vaccines for efficacy and safety.[14] Vaccines enable the immune system to recognise the antigens of microorganisms and mount a powerful immunological response by creating antibodies against the pathogens when they are delivered into the human body.[34] This prevents the pathogen from replicating after infection and consequently the disease from developing. As a result, vaccine research is critical for avoiding the spread of SARS-CoV-2 infection and aiding in the reduction of COVID-19 morbidity and mortality. COVID-19 vaccines that work should be exceedingly safe and pure, with great efficacy and potency. In this case, a vaccine candidate should go through three stages of human clinical testing. Phase I, Phase II and Phase III of the vaccine development pipeline are completed in order, followed by licensure. Phase IV studies aid in the continual monitoring of the candidate vaccines' safety and immunogenicity. In the traditional method, a vaccination could take up to 10–15 years to reach the public. However, the present unusual scenario has prompted the use of expedited vaccine development tactics.[34] There are 29 vaccinations in Phase I trials, 40 vaccines in Phase II trials, 27 vaccines in Phase III trials and 13 vaccines that have been licensed by at least one country as of 15 March 2021.[35] The Oxford/AstraZeneca COVID-19 vaccine has been recommended for use in Nigeria by the National Agency for Food and Drug Administration and Control.[32] The vaccination should be administered in two doses, 8–12 weeks apart. When the second dosage of the vaccine is given, the vaccine's efficacy is increased.

Vaccination has always been plagued by vaccine reluctance, despite the huge benefits it has provided since Edward Jenner's first discovery of the smallpox vaccine until now, saving millions of lives globally at a relatively low cost. Nigeria is Africa's most populous country, with a complicated history of vaccine apprehension. Despite vaccinations' established effectiveness and safety, an increasing number of people believe they are dangerous and unnecessary.[26]

An adverse event following immunisation (AEFI) is any undesirable medical incident that occurs after immunisation but may not always have a causal association with vaccine use.[36],[37],[38],[39] Any unfavourable or unexpected sign, aberrant test finding, symptom or disease might be considered an adverse event.[40],[41] Adverse reactions can range in severity from minor side effects to life-threatening reactions, and they can raise public concerns about vaccine safety. All vaccinations used in national immunisation programmes are safe and effective when used correctly under approved conditions.[42] In practice, however, no vaccine is fully risk-free, and adverse reactions to vaccinations do occur infrequently.[43]

In adults of all ages, the advantages of AstraZeneca outweigh the risks; most side effects are minor to moderate and resolve within a few days; nevertheless, very rare incidences of blood clots with low blood platelets have occurred following immunisation.[44] This led to some countries temporarily suspending its use,[45] however we have no published data on AEFI of this vaccination in our population. Hence, this study aims to identify the AEFI associated with the COVID-19 vaccine in Rivers State as the vaccination process commences to further enable the risk-benefit analysis of the COVID-19 vaccination programme.

  Subjects and Methods Top

Study design and participants

A cross-sectional study design was adopted. The study participants were adults from 18 years old and above in Rivers State who received the first dose of the COVID-19 vaccine from 16 March 2021.

Data collection

Data were collected using a WHO adapted COVID-19 reporting form for AEFI and this was done between 31March and 30 April 2021 within 28 days of participants receiving the vaccine. The structured, close-ended, pretested questionnaire was a telephone-based and web-based survey form filled by the COVID-19 vaccine receivers who had been randomly selected using simple random sampling method. Phone calls were placed to the individuals by the researchers and responses were filled instantly via KoboToolbox. It had three sections which provided information on the socio-demographic characteristics of respondents, the adverse events following COVID-19 vaccination and the risk perception of the respondents.

Sample size and sampling technique

Sample size for this study was calculated using the formula,[46] (n = Z2P [1 − P]/d2). The following assumptions were made while calculating the sample size; the confidence level was 95% (z = 1.96), the margin of error (d) set at 0.05, the estimated prevalence (p) chosen to be 50% (P = 0.5). The calculated sample size was 441 (considering 15% non-response). A multi-stage sampling method was applied, first, 13 Local Government Areas (LGA) were selected from the 23 LGAs in the state using simple random sampling method by balloting. Simple random sampling method using a random number generator software was used to select participants in the study from a sample frame of 5745 vaccinated persons provided by the Monitoring and Evaluation officers and Medical Officers of Health from the 13 LGAs selected.

Data analysis

Data were entered and cleaned in excel and exported to the IBM SPSS statistics software version 23 (IBM Corp., Armonk, NY, USA) for analysis. Descriptive analysis was performed to describe the frequency and percentage of study participants' socio-demographic characteristics and post-vaccination events. Chi-square test was used to test for association between adverse events and age, allergy, medical history and management of AEFIs.

Ethical approval

The ethical approval was obtained from Rivers State Health Research Ethics Committee on 31 March 2021 with protocol number RSHMB/RSHREC/11.21/VOL. 8/080. The purpose and benefits of the study were explained to each study participant. To keep confidentiality, all identifiers were removed.

  Results Top

This study was done to identify the AEFI associated with the COVID-19 vaccine in Rivers State. A total of 428 respondents participated in this study out of the calculated sample size of 441, giving a response rate of 97.0%.

Socio-demographic characteristics

Out of 428 participants, 56.1% were males and 43.9% were females. The mean age for all respondents was 42 years. Forty-six percent (46%) and 37.1% of participants were within the age range of 30–44 and 45–59, respectively, 9.8% were within the age range of 18–29 and 7% were aged 60 years and above. More than half of the participants (78.3%) had tertiary education; 28.5% were health workers with the majority (56.1%) being non-health workers and the rest 15.4% were unemployed [Table 1].
Table 1: Classification of the study participants according to their socio-demographic characteristics

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Post-vaccination adverse events

In the study, out of 428 participants, 216 (50.5%) reported post-vaccination adverse events. Out of 216 participants who recorded adverse events, only 10 (4.6%) were severe and of the 10 participants whose adverse events were severe, 30% recorded it as life-threatening, 60% were hospitalised and 10% were placed on bed rest [Table 2].
Table 2: Prevalence of adverse events following coronavirus disease-19

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An extensive range of potential post-vaccination adverse events was assessed among the 216 participants who reported post-vaccination adverse events and the most common adverse events were mild fever (47.2%), pain at the injection site (41.2%), fatigue (33.3%), moderate fever (21.2%), body ache (17.5%), headache (13.8%) and dizziness (13.8%) [Figure 1]. Concerning the time required for adverse effects to start, participants' responses in [Figure 2] showed that adverse events mostly emerged <24 h after vaccination (62.2%). About 58 (26.8%) participants reported that adverse events started immediately after vaccination, while 17 (8.3%) after 1 day [Figure 2]. Furthermore, 44% stated that these adverse events lasted for <1 day, 48.6% for 2 to 3 days and 7.4% for more than 3 days. To ease post-vaccination adverse events, 36.1% took pain killers, 9.2% used homemade remedies and most of the participants (46.7%) took no medication [Table 3].
Figure 1: Frequency of adverse events following COVID-19 vaccination

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Figure 2: Frequency distribution of onset of adverse event(s)

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Table 3: Frequency distribution of participants acts to reduce adverse event post-vaccination

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The Chi-square test showed that there was no significant association (P = 0.14) between age and the presence of adverse events [Table 4]. The Chi-square test showed that the methods taken to ease post-vaccination adverse events were significantly associated with how long the adverse event lasted (P ≤ 0.001) [Table 5]. There was no significant association (P = 0.216) between the history of allergy and the severity of adverse events [Table 6]. There was no significant association (P = 0.150) between preexisting health conditions and the presence of severe adverse events [Table 6].
Table 4: Association of age with the prevalence of adverse event following coronavirus disease-19 vaccination

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Table 5: Association of management of adverse events with how long it lasted

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Table 6: Association of allergy and pre-existing health condition with severe adverse event

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Findings also revealed the participants' risk perception of the COVID-19 vaccine before vaccination. A higher proportion of the participants 160 (37.4%) had very low-risk perception of the vaccine, 108 (25.2%) had moderate-, 97 (22.7%) had low- and 63 (14.7%) had high-risk perception of the vaccine. Of the 428 participants in this study, 91.1% said yes to taking the second dose of the COVID-19 vaccine, 7.0% were undecided and 1.9% said no to taking the second dose.

  Discussion Top

In the present study, males (56.1%) were more than females. This finding is similar to a study carried out in south-south Nigeria involving 1000 participants that showed that male participants were two times more likely than women to get the COVID-19 vaccine.[30] Another study done among Nigerian adults also showed that male was a positive predictor of COVID-19 uptake.[47] This might be because women in Nigeria are more faith based and more likely to believe in myths.

The highest number of people who were selected were in the 30–44 and 45–59 years of age category. Not surprisingly, more than half (78.3%) of the participants had tertiary education as their highest educational attainment. Before vaccine availability, several studies had assessed the acceptance of COVID-19 vaccines in Nigeria. A study done among Nigerian adults showed that out of 451 respondents who were willing to receive the vaccine, 96.4% had tertiary education and being male was a positive predictor of COVID-19 vaccine uptake.[47] This may not be unrelated to the fact that educated people have more access to correct information and are less likely to believe rumors and myths.

In this study, 50.5% of participants reported post-vaccination adverse events, however, according to studies carried out in Nepal[33] and Jordan[48] on adverse events following the AstraZeneca vaccine, 85.04% and 88.9% reported post-vaccination adverse effects, respectively. This could be because of the people's perception since the study was self-reporting. It could also be due to the quality of that particular batch of vaccine given at the time of the study.

Similar to findings recently published by Hatmal et al.,[48] the most common post-vaccination adverse events were mild fever (47.2%), pain at the injection site (41.2%), fatigue (33.3%), moderate fever (21.2%), body ache (17.5%), headache (13.8%) and dizziness (12.0%).

Most of the participants in this study (62.2%), reported adverse events that started <24 h post-vaccination and resolved in <3 days (77.4%). This is also similar to the study by Hatmal et al.[48] which showed that adverse events mostly appeared within 9–12 h of vaccine injection (35%). Around 26% of participants reported that adverse events started after 5–8 h, while 15% within up to 4 h. Furthermore, more than half of them (56%) stated that these adverse events lasted for one to 3 days, and 30% for <1 day. This may imply that all vaccines work in a similar way of causing mild effects some hours after receiving it which shows that the body is building immunity against the disease.

A significant association was found between the duration of adverse events and methods participants used to manage these events such as taking painkillers and using homemade remedies (P = 0.014). Participants who took any form of treatment were less likely to get better in <3 days compared to those who had no treatment. This may be because Nigerians have a habit of waiting out symptoms to see if they will resolve by themselves before taking any form of treatment.

There was no significant association between age and adverse events following vaccination (P = 0.05). This finding is similar to that done in Nepal[33] where no significant association was found between age and AEFI (P = 0.05) but was different from a study carried out in Korea[49] which found that the chance of having symptoms decreased with advancing age. From the findings in this study and other studies mentioned here, it may imply that there is no clear-cut association between age and AEFI, hence with further studies, this uncertainty can be settled. We also did not observe a statistically significant association between the incidence of severe AEFIs and participants with allergies or medical history.

Before getting the COVID-19 vaccination, some of the participants in this study were afraid of it (39.9%). However, after vaccination, the overall picture altered considerably; most of the individuals felt more at ease and even elected to have a second dose (91.1%). With this in mind, it appears that if a country undertakes its own independent studies on the safety of COVID-19 vaccinations, conducted by local researchers, public confidence in the vaccines will improve, accelerating the COVID-19 immunisation process.

Study limitations

The study's limitation was its reliance on telephone-based self-reporting for data collection. Recall bias could have limited the study since participants were interviewed between a day and 28 days after receiving the vaccine. This also excluded the identification of any potential long-term risk of vaccination. The difficulty of retrieving vaccination data from the LGAs at the time of this study was also a limitation.

  Conclusions Top

The adverse events associated with the AstraZeneca vaccine were largely mild to moderate and resolved within a few days which showed that the approved COVID-19 vaccine has a good safety profile. Among the modest participation in Nigeria's national vaccination campaign, the findings of this study may be of interest to the Ministry of Health since they can be used during its directed efforts to improve knowledge of the safety, effectiveness and benefits of the COVID-19 vaccine.


We would like to provide our profound thanks to the M&E in Rivers State for support. The authors acknowledge the data collectors, supervisors who were involved in this study. Finally, we thank the study participants involved in this study.


The results of this study show that the COVID-19 vaccine has a good safety profile. The government should therefore increase vaccination awareness in the state to change residents' perceptions of the vaccine and increase vaccine uptake.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

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  [Figure 1], [Figure 2]

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]


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