The DTwP (Diphtheria, Tetanus toxoids and whole-cell Pertussis) vaccine commonly causes mild to moderate side effects such as redness and swelling of the injection site, pain, fever and so on. The pertussis component of this vaccine especially is responsible for the DTwP adverse events.1 Incorrect injection technique can also cause or exacerbate these adverse events. For example, if the DTwP vaccine is not injected deep intramuscularly and some of the aluminum salt used as an adjuvant in vaccine is injected subcutaneously, then local adverse events will be increased.2 It is clear that other characteristics of the needle such as length,3 diameter4 and sterility status can influence the local adverse events. At present, in Iran, Auto-Disable (AD) syringes are being used to implement universal immunization precautions, although other types of syringes are available in the immunization units. AD syringes in Iran are purchased by the Ministry of Health and Medical Education and are provided to all units of the immunization services.
Findings of adverse events following immunization (AEFI) surveillance system indicate increasing cases of local adverse events following DTwP immunization (unpublished data). The number of severe local reactions following immunization with DTwP reported as 36, 25 and 21 cases in first, second and third year before the study. Part of the increase in incidence of these side effects can be attributed to improvement in reporting. However, the increase in mild adverse events led health care workers to believe that AD syringes were the main cause. Many health workers often complain about AD syringes and prefer to use the regular syringe. Given that the use of the AD syringes is recommended by international agencies, it is very important to determine the effect of using this syringe on post-immunization adverse events. On the other hand, the needle used in the AD syringes has a length of 25 mm and a 23 gauge diameter, and some health care workers assuming that thinner needles cause less pain and adverse events for infants tend to use the routine syringes with a thinner needle (24 gauge). To our knowledge, there is no other study which has investigated comparison of different syringes and needle gauges on adverse events following DTwP immunization. A clinical trial was required in order to clarify the role of the syringe type in AEFIs, and this study was conducted to address this important question.
MATERIALS AND METHODS
This study is a triple-blind, multicenter clinical trial, using a 1:1 randomized block design, and was conducted in Shahroud city, northeast of Iran. In this study, children who are eligible to receive DTwP vaccine were randomized, and local adverse events after DTwP immunization were assessed in the 2 groups that used 2 syringe types for immunization (equivalence study). The study protocol was registered in the Iranian Registry of Clinical Trials (http://www.irct.ir/) with code IRCT201107317171N1.
All children who needed the DTwP vaccine were eligible for inclusion in the study in 4 primary health care centers. According to national guidelines, the DTwP vaccine will be injected 5 times (at 2, 4, 6, 18 months and 6 years of age). The children participating in the study had no contraindication for DTwP immunization. After explanation of the project by the trained health care worker and the need for the children to be examined thrice at their own homes, the children were included in the study on parental consent and the signed the informed consent form was received along with the assurance of no intention to travel within the next 6 days. Otherwise, the children were vaccinated according to the national guideline for immunization. After inclusion of the child in the study, his or her profile (with the latest address and telephone number) was filled up in a form. The health care worker then announced the child’s name to the person who registered the children by phone and asked for the syringe type used for immunization. Finally, a copy of the informed consent form, containing the specifications and phone number of one of the project executives, was delivered to the parents, and in addition to the common recommendation after immunization, it was emphasized that if they were unwilling to participate in the study at any time in the future, they could be excluded. Every day, the health experts received the forms of the children included by referring to the health care center, and they visited the children’s homes using the contact details to investigate the AEFI. These experts were unaware of the type of syringe used.
The DTwP vaccine used was the same one employed in the routine immunization program at the time of conducting this study. This vaccine was manufactured by Serum Institute of India (Hadapsar, Pune, India), batch number 027P1008A, production date June 2011 and expiry date May 2013. The syringe used in the intervention group was 1 mL syringe with a 24-gauge, 25-mm needle made by KFT Safegard Medical (Farkaslyuk, Hungary) with LOT NO: 2009 41 and expiry date October 2014. This syringe meets the requirements of European Conformity (CE marked) in accordance with the Medical Devices Directive 93/42/EEC. The control group received the AD syringe used in the routine immunization programs in Iran. These 0.5 mL syringes was produced by Yazd Syringe Co. (Yazd, Iran) with a 23-gauge, 25-mm needle, batch number 3834-K0 B-03, production date March 23 2010 and expiry date March 23 2013. In children below 2 years of age, all the vaccines were injected into the lateral thigh muscle (vastus lateralis) and the second booster doses were injected into the deltoid muscle.
The primary endpoint in this study was a severe local reaction, which according to international definitions5 means, redness and/or swelling centered at the site of injection and one or more of the following:
- - swelling beyond the nearest joint,
- - pain, redness and swelling of more than 3 days’ duration, or
- - requiring hospitalization.
Given that it is difficult and imprecise to assess pain in infants below 1 year of age, in this definition, redness and swelling that lasts more than 3 days, whether it is combined with pain or not, was regarded as the second of the criteria listed above. The injection site redness, swelling and induration were measured by the health experts with a precision of 1 mm on days 2, 4, and 6 after immunization at home visit of infants. The axillary temperature was measured with digital thermometers with a precision of 0.1°C. The accuracy of the thermometers was examined every week, comparing them with mercury thermometers. Axillary temperature is 1 degree less than rectal temperature6 and the latter method is preferred for fever measurement in infants, so all children with axillary temperature ≥37°C and/or those that their parents had reported fever in the child were considered febrile. Similar to other measurements, the axillary temperature was measured by the health experts on days 2, 4, and 6 after immunization at home visit of infants.
Other adverse events of DTwP vaccine, such as prolonged crying, vomiting, irritability and anorexia, were obtained by interviews with the parents. Any child suspected to have abscesses was examined by a physician. Primary and secondary endpoints were investigated at intervals of 48, 96 and 144 hours (days 2, 4 and 6) after immunization by the health experts at the children’s homes. If the child had no symptoms on days 2 and 4, the assurance on the lack of AEFIs on the 6th day was ascertained by phone.
Considering that alpha and beta were equal to 0.05 (confidence level of 5% and power of 95%), the prevalence of severe local reaction was equal to 20%, and expecting that this study could determine a 10% difference in this prevalence, the sample size was determined from 484 children in each group. We conducted the study on 500 children in each group. Randomization was performed in 4 separate centers, and up to 300 children in each were allowed to participate in the study.
The balanced block randomization method was used to randomly divide the children into 3 groups, stratified by site. Central telephone randomization was used for allocation concealment. With the introduction of each eligible child to the health expert by phone, the syringe used was declared to the vaccinator and the child was registered in the trial. Each child in the health centers was given a serial number, and only after decoding, the syringe used for their immunization would be known. The allocation expert would keep the code list of each center confidential until the end of the trial analysis.
While conducting the steps mentioned above, experts who investigated the immunization adverse events and the biostatistician (each case described as being in group A or group B) were blind to the intervention type in each group, which in turn minimized the bias. Even the children who received the vaccine and their parents were blind, and only the vaccinators were aware of the syringe type during the intervention, which had no role in the next follow-ups and results recordings.
The frequency of the primary endpoint variable (severe local reaction) was calculated in both groups, and then the risk difference and risk ratio were calculated with 95% confidence intervals (CIs). This analysis was performed for all the children and the children in each sampling center to assess the internal validity.
A similar analysis was also performed for the secondary endpoints studied on days 2, 4 and 6 after immunization. Considering the 3 times examination of each child (repeated measures), using generalized estimating equation, the odds ratio was calculated for each secondary endpoint with 95% CIs. Given the dichotomous nature of the secondary endpoints, Logit link was used in the generalized estimating equation model. The analysis of variances for repeated measures was used to compare redness and swelling diameters in 2 groups.
The prevalence of the various local and systemic adverse events was investigated as an additional analysis by calculating the percentage of adverse events in the various age groups and at different times after immunization.
The time to maximum occurrence of redness and swelling in 2 groups is investigated, using the KaplanMeier survival analysis.
In the 4 health centers, 1000 children were selected consecutively from among those who needed immunization (1700 children) and had inclusion criteria and their parents signed informed consent to participate in the study. Follow-up could not be done for only one child; therefore, the remaining 999 children in the 4 centers were eligible for analysis. Comparison of vaccine times between participated and not-participated children showed no differences. Randomization details in the 4 centers and the children in each group are shown in Figure 1.
From February 20, 2011, to May 10, 2012, 1000 eligible children in 4 health centers in Shahroud (located in northeast Iran) were randomized into 2 groups: vaccinated with the AD syringe and vaccinated with the alternative syringe. These children were examined in terms of the AEFI on days 2, 4 and 6 after immunization (health workers recorded the required data by visiting the children at their homes).
Considering 1 case of loss to follow-up, among the 999 children studied, 487 subjects (48.7%) were male and 512 subjects (51.3%) were female. The sex ratio in the 2 groups was not different (P = 0.728). The average age of the children vaccinated with the AD syringe was 13.6 months with a standard deviation (SD) of 19.4 and that of children vaccinated with the alternative syringe was 13.5 months with an SD of 19.2 months. The difference between the mean age was not significant (P = 0.933), and no significant differences were observed in the number of children at different scheduled times of immunization in the 2 groups (P = 0.498). Further details regarding the basic variables are presented in Table 1.
The severe local reaction occurred in 21 children (2.1%). This outcome was 2.0% in the children vaccinated with the AD syringe and 2.2% in the children vaccinated with the alternative syringe. This difference was not significant (Table 2). No difference in this outcome between the 2 groups in each sampling center also confirms the lack of effect of the syringe type and needle gauge on the occurrence of severe local reaction. Among the 21 children with severe local reaction, the incidence of redness, swelling, and pain and swelling more than 3 days of duration was almost equal in AD and alternative syringes groups. While the AD group had a lower rate of redness with more than 3 days duration than the other group (5 cases compare to 8 cases, risk ratio = 0.63, CI 95%: 0.21–1.9), children vaccinated with alternate syringes had 2-fold more incidence of swelling beyond the nearest joint (6 compare to 3 cases, risk ratio = 2.0, CI 95%: 0.5–8.0). These differences were not statistically significant.
Investigating the other adverse events following the DTwP immunization (secondary endpoints) showed that the syringe type and needle gauge had no effect on the occurrence of such adverse events. The incidence rate, risk difference and relative risk of these adverse events are summarized in Table 3. Similar findings observed in analysis of secondary endpoints in generalized estimating equation model, even after controlling the confounding effects of age and previous doses of DTwP vaccine (Table 4). These findings were observed even after stratifying subjects into those who were recipients of only primary immunization doses versus those who received booster doses.
Analysis of variances for repeated measurement of redness and swelling in the days of assessment of adverse events showed that the average extent of redness and swelling is higher when using the AD syringe compared with the alternative syringe. Nevertheless, these differences are not significant (Table 5). The extent of redness and swelling significantly decreased with increase in days after immunization.
This study was an opportunity to investigate incidence rate of the adverse events following DTwP immunization in an acceptable sample size. As summarized in Table 6, the most common local adverse events on the second day include pain (26.2%), redness (17.7%), swelling (15.7%) and injection site indurations (16.3%). The occurrence of all these adverse events was observed more during the injection of the DTwP vaccine booster dose and on the second day after the immunization, except for the injection site indurations.
The maximum diameter of redness and swelling was recorded in day 2 after immunization, and there were no significant differences between 2 groups in this regard (Table 7 and Fig. 2).
This study showed that the occurrence of mild and severe local AEFI with the DTwP vaccine was not related to the type of syringes and needle gauge used for immunization. According to the World Health Organization Guidelines for intramuscular injection of vaccines, needles with a diameter of 23 or 25 gauge and a length of 25 mm should be used. With respect to this instruction, this study showed that the needle diameter (23 or 24 gauge) had no effect on the AEFI. In this study, we used a syringe of identical length (25 mm) to comply with the national and international guidelines. Moreover, the review studies also emphasized the use of needles of 25-mm length for this type of immunization.3 Our results are consistent with the results of other researchers in India.7 However, other studies have observed slight differences in the immune response and local adverse events between needles of the same length but with different diameters.4 In a few studies that assessed the influence of needle diameter on AEFIs, a comparison was done between the needle diameters of 23 and 25 gauge, while in our study, the needle diameters used were 23 and 24 gauge.
In a trial study, Wiesenthal et al.8 concluded that a change in the needle does not affect the local and systemic adverse events of the vaccine and that cleaning the needle with sterile gauze increases the systemic adverse events. Further clinical trials mainly investigated the immunogenicity of the various types of vaccines or the adverse events of the different vaccines by different types of vaccine administration.9–11
Three examinations of the AEFIs determined the behavior of each adverse event studied in terms of duration and time of maximum occurrence. This finding has been less considered in other studies. In fact, AEFIs are often assessed during a special time period of 24 hours to 7 days after immunization. This is one of the reasons for the different findings in the frequency of the AEFIs in various studies.
Common adverse events following DTwP immunization were reported more frequently from several studies in Iran.12–16 In addition to the time of investigation of the adverse events, the research methodology, age group of children and the injection site of the vaccine are important factors in the occurrence of AEFIs. For example, in one study, 42.3% of DTwP vaccine was injected into the buttock,15 whereas in this study the DTwP vaccine was injected only into the thigh and deltoid muscles. Fever occurrence in our study is less than in other studies and even the WHO immunization references.17 This may be due to the temperature measurement in the axillary area. Studies show that this method has the lowest reliability,6 and the WHO instructions have recommended a rectal measurement. However, this may be due to the time of the first investigation, on the second day after immunization, and also because 12.6% of children in the investigation were taking acetaminophen on the second day. Another reason for the low incidence of fever in this study can be attributed to the exact implementation of the immunization guidelines and standards by the health care workers. In most studies used for comparison, the measurement method and the definition of fever are not clear. Only one case (0.1%) of abscess was found, which is lower than the results recorded in similar studies. Similar to this study, some studies in the Middle East countries have reported the incidence of various AEFIs to be lower than the international statistics.18
Considering the low occurrence of the primary endpoint (severe local reaction), if the sample size was greater, the conclusion could be made more precisely and this may be considered as a limitation of this study. In this study, blinding the vaccinators was not possible. However, by selecting an appropriate randomization method, the vaccinators were unaware of the syringe type used until the moment of immunization and could not guess it. The descriptions given in recruitment section indicate that the randomization was effective. Thus, the strengths of the study include using the correct randomization and concealment technique, good follow-up of children by visiting them at their home 3 times and the continuous monitoring of the study.
Considering that children of both sexes (in approximately equal ratio) in different age groups participated in this study and that immunization was done with all 3 doses of DTwP vaccine and 2 booster doses, the results of this intervention can be generalized for all children below 6 years of age who received the DTwP vaccine
This multicenter, randomized controlled trial showed that the occurrence of the local adverse events following DTwP vaccine is not related to the syringe type and needle gauge and, generally, all these local adverse events have a relatively low incidence. Considering the higher occurrence of redness, pain and swelling in older children, it can be suggested that the vaccine with acellular form of Pertussis (DTaP), which has fewer systemic and local adverse events,19,20 be used for immunization, at least for booster doses of DTwP vaccine.
This study, No. 9033, was an approved proposal in the Shahroud University of Medical Sciences. The authors express their gratitude to the Vice Chancellors for Health and Research of the Shahroud University of Medical Sciences who made a valuable contribution to the approval and implementation of this project.
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