Visas and vaccinations: All travelers must present the International Certificate of Vaccination against yellow fever, if they are coming from countries defined by PAHO/WHO as having active transmission and at this time:

• Argentina, Bolivia, Brazil, Colombia, Ecuador, French Guiana, Panama, Paraguay, Peru, Venezuela and from the African Continent, all countries, Tanzania, Sao Tome and Principe and Somalia.

You need a type "B" visa. It is understood by Consular Visa or Without Consultation those extended by the accredited Diplomatic or Consular official without requiring prior authorization from the Ministry or Secretariat of Foreign Affairs or the General Directorate of Migration and Foreigners.

• If you have a U.S. visa you will not need a visa to enter Nicaragua. 

Documents to present: 

1. Visa in stamped in the valid passport with a minimum of six (6) months.
2. Vaccination card against yellow fever, in case of coming from a country at risk (mentioned above).
3. Economic solvency.
4. At the entrance to the country, to cancel tourism tariffs, according to the General Law of Tourism (tourism card of 10 dollars Attention: To have the $10.00 in cash, since the migratory authorities do not accept any other form of payment), here.
5. Complete the "Entry Request" form. This requirement is for all foreigners entering Nicaragua by air, sea or land. The form must be filled out and sent to the following e-mail address: solicitudes@migob.gob.ni . It is recommended to send the application with as much time as possible. Once the application is resolved, the corresponding Border Post(s) and the applicant(s) will be notified. You can also download the form here.
6. Any other requirements that you are required to present at the time of entry into the country and that are presented at the time of your visa application.
7. It is at the discretion of the immigration authority the number of days to be granted for your stay in the country.
8. Children under 03 years of age are exempted from this requirement, i.e. they will not be asked to enter the country or vaccination schedule or PCR test. These requirements are only indispensable for travelers over 03 years of age. More details here.

More details, here.

More Information, here.