The possible adverse events following immunization with pentavalent vaccine are generally mild: serious reactions are very rare (see Section 2.2.6). The mild reactions are:

Soreness. Some children may develop mild soreness, redness, or swelling at the injection site, but this will go away within 1–3 days.
Fever. Some children may develop a mild fever (a temperature of around 37.3^oC to 38.4^oC, measured with a thermometer in the child’s armpit, is termed a low-grade fever). It should disappear within a day. Fever that begins more than 24 hours after a pentavalent injection is unlikely to be a reaction to the vaccine and should be investigated.
Crying for more than three hours, mostly because of pain, occurs in up to 1% of infants.

A serious but rare adverse event is an abscess, which may develop a week or more after immunization (Figure 2.5), usually because an unsterile needle or syringe was used, or the vaccine was not correctly injected into the muscle. The management of these adverse events at Health Post level is summarised in Table 2.4.

Figure 2.5 An abscess caused by an unsterile needle or syringe, or incorrectly administered pentavalent vaccination. (Source: WHO, 1998, Immunization in Practice, Module 2, EPI Vaccines, Figure 2-C, p.8)

Table 2.4 Management of adverse events following immunization with pentavalent vaccine at Health Post level.

Adverse event	Management	Comments
Low-grade fever (37.3^oC to 38.4^oC)	Paracetamol syrup, 5 ml as required, up to a maximum of four doses	Will usually disappear within a day
Pain and soreness at the injection site	Paracetamol as above; warm compress (a warm cloth or another warm material) applied under pressure to the sore area of skin and held in place for some time	Will usually disappear within a day
Abscess at the injection site	Amoxicillin syrup orally three times daily	Refer the child urgently to the next higher health facility