From Wikipedia itself:

Wikipedia articles should be based mainly on reliable secondary sources, i.e., a document or recording that relates to or discusses information originally presented elsewhere.

[...]

Primary sources are often difficult to use appropriately. Although they can be both reliable and useful in certain situations, they must be used with caution in order to avoid original research. Although specific facts may be taken from primary sources, secondary sources that present the same material are preferred. Large blocks of material based purely on primary sources should be avoided. All interpretive claims, analyses, or synthetic claims about primary sources must be referenced to a secondary source, rather than original analysis of the primary-source material by Wikipedia editors.

When editing articles in which the use of primary sources is a concern, in-line templates, such as {{primary source-inline}} and {{better source}}, or article templates, such as {{primary sources}} and {{refimprove science}}, may be used to mark areas of concern.

In other words, if you don't have any secondary sources, primary sources are also OK, they should just be used with caution.