The side effects of the yellow fever vaccine are generally mild and include fever, headache, muscle pain, fatigue, and injection site reactions such as redness or soreness. Approximately two thirds of people who receive the yellow fever shot don't notice any side effects at all.
Injection site redness and soreness
Minor injection site issues affect about 1 out of 5 patients[1]. You should be fine taking an over-the-counter pain medicine or anti-inflammatory medicine to address these symptoms, however the effects of these medicines on the vaccine-related immune response has not been fully studied, so you should take them only if necessary.
Fever, headache, muscle pain
Approximately 1 out of 3 patients experience headache, fever and/or full body muscle pain though these are typically very mild in nature[1]. You should drink plenty of fluids and rest if you experience these symptoms. There is a debate over whether it is okay to take pain relief medications and anti-inflammatory medications to deal with vaccine side effects. We don't have a lot of information about it. Generally, try to avoid them but taking them is probably fine.
How likely are side effects to occur?
According to a study of 60 travel clinic patients in the Netherlands[1], side effects don't seem to vary much between young patients and elderly, with the primary difference being that younger patients may be more likely to experience redness at the injection site (p = .05). Fever and full-body muscle pain are also slower to set in for elderly patients (median = 5 days) than for younger patients (median = 0.5 days; p=.002).
Injection site adverse events (redness, swelling and/or pain) were present in 30% of young patients and 14% of elderly patients and lasted only the first few days after getting the shot.
Most importantly, fever and/or full-body muscle pain occurred in 40% of young people and 29% of elderly patients.
While these numbers may seem high, it's important to note that since there was no control group, we don't know how many of these people would have gotten sick anyway without getting the shot during the same period. In a separate study in Brazil, they matched the yellow fever vaccine up against a placebo[2] and found the following:
Compared to placebo, the excess risk of any local adverse events ranged from 0.9% to 2.5%
Compared to placebo, the excess risk of any systemic adverse events (headache, fever, etc.) ranged from 3.5% to 7.4% across vaccine groups.
The excess risk of events leading to search for medical care or to interruption of work activities ranged from 2% to 4.5%.
Viremia, the presence of the virus in the blood, was detected in 3%-6% of vaccinated people up to 10 days after vaccination.
In extremely rare cases, more serious side effects can occur, including an allergic reaction or a neurological condition called yellow fever vaccine-associated neurotropic disease (YEL-AND). However, these severe side effects are extremely rare. If you experience an allergic reaction to the vaccine after you leave the vaccination clinic you should immediately seek emergency medical attention.
Who needs to get the yellow fever vaccine?
The yellow fever vaccine is recommended for individuals who are traveling to or living in areas where yellow fever is endemic or poses a risk. It is especially important for individuals traveling to certain countries in Africa and South America where yellow fever is prevalent. Additionally, some countries may require proof of yellow fever vaccination for entry, known as a yellow fever certificate.
Sources
1. Roukens, Anna H., Darius Soonawala, Simone A. Joosten, Adriëtte W. de Visser, Xiaohong Jiang, Kees Dirksen, Marjolein de Gruijter, Jaap T. van Dissel, Peter J. Bredenbeek, and Leo G. Visser. "Elderly subjects have a delayed antibody response and prolonged viraemia following yellow fever vaccination: a prospective controlled cohort study." PLoS One 6, no. 12 (2011): e27753.
2. Camacho, Luiz Antonio Bastos, Savitri Gomes de Aguiar, Marcos da Silva Freire, Maria da Luz Fernandes Leal, Jussara Pereira do Nascimento, Takumi Iguchi, José Azevedo Lozana, and Roberto Henrique Guedes Farias. "Reactogenicity of yellow fever vaccines in a randomized, placebo-controlled trial." Revista de Saúde Pública 39 (2005): 413-420.