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in the number of unvaccinated susceptible individuals

who enter or live in endemic areas. This leads to the im-

mediate call for action by health authorities in order to

contain the disease’s progress through blocking vaccina-

tion campaigns.

mmunization

In 1937, an attenuated virus vaccine, specific for yellow

fever, was developed conferring lifelong immunity in up

to 99% of those vaccinated. Max Theiler, of the Rockefel-

ler Foundation, received in 1951 the Nobel Prize of Med-

icine for such discovery.

Since then, vaccination cam-

paigns in endemic countries have been the central axis

that has significantly reduced the number of cases in the

world and in Brazil.

Today, being vaccinated against yellow fever is a con-

dition for entry into several countries due to the risk of

contracting the disease at the destination or the possibil-

ity of introducing the virus into an epidemiologically

compatible environment.

In Brazil, two vaccines are distributed against yellow

fever, one produced by Biomanguinhos (Fiocruz) and

another by the Sanofi-Pasteur laboratory. For the list of

centers authorized to issue an official vaccination docu-

ment, visit the website of the National Health Surveillance

Agency,

www.anvisa.gov.br

. For the list of countries re-

quiring vaccination against yellow fever as a condition

for issuing the entry visa, visit the World Health Organi-

zation website, or the US Centers for Disease Control and

Prevention, www.who.int and www.cdc.gov/travel, respec-

tively. Travelers with contraindications to the vaccine and

who are going to countries that require the Internation-

al Certificate of Vaccination against Yellow Fever must

present a medical statement attesting to the fact to one

of the authorized centers for the emission of the vaccine

exemption affidavit form, valid internationally.

The yellow fever vaccine consists of attenuated live

virus, strain 17D, with two sub-strains: 17DD, used in

Brazil, and 17D-204, used in other countries. Protection,

which reaches levels above 95%, begins after the tenth day

of application and probably extends for decades. Current

evidence shows that the protection conferred by the vac-

cine is long-lasting, probably lifelong, and therefore there

is no recommendation for revaccination, even if there is

new displacement to endemic areas.

Contraindications

include: children under 6 months of age; gestation; im-

munosuppression associated with disease or therapy

(cancer, including lymphomas and leukemias, AIDS, sys-

temic corticosteroid therapy, chemotherapy and radio-

therapy), previous history of egg anaphylaxis, and allergic

reaction to the previous dose of the vaccine. For those

with contraindications, regions where the disease is en-

demic should be avoided; if the trip is essential, follow

the methods of individual protection against mosquitoes.

Non-serious reactions are common, including pain

at the site of application, fever, myalgia and headache,

which generally appear after vaccination between the

second and fifth day after receiving the dose. Serious

adverse events such as yellow fever vaccine-associated

viscerotropic and neurotropic disease, although infrequent,

may arise. Cases similar to the disease, with visceral in-

volvement, have been described since 1996, with an ap-

proximate incidence of 1 for every 40,000-50,000 doses

in the United States, especially in individuals over 60 years

of age, with mortality around 65%. Likewise, rare cases of

encephalitis have been reported, with a higher frequency

in children, particularly those under 6 months. Such

occurrences are probably linked to individual immune

responses and not to changes in the vaccine virus. The

fact that four of the 62 cases of viscerotropism already

reported in the world (up to the year 2016) were linked

to diseases leading to thymus dysfunction or previous

thymectomy corroborates this assumption.

eferences

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2. Goldani LZ. Yellow fever outbreak in Brazil, 2017. Braz J Infect Dis.

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3. Ortiz-Martínez Y, Jiménez-Arcia LF. Yellow fever outbreaks and Twitter:

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Norrby E, Prusiner SB. Polio and Nobel prizes: looking back 50 years. Ann

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Paules CI, Fauci AS. Yellow Fever – Once Again on the Radar Screen in the

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