 Patients suffering from rheumatoid polyarthritis have an increased risk to develop an infection compared to general population, with a more important mortality risk because pneumococcus is considered as one of the major pathogenic agents. Antipneumcoccal vaccination is recommended to patients suffering from chronic inflammatory rheumatism treated with immunosuppressants. Methotrexate is a long term treatment used in first intention for rheumatoid polyarthritis. A recent study shows a decrease of efficacity of antipneumoccal vaccination for patients suffering from rheumatoid polyarthritis treated by methotrexate. The tested hypothesis will be the presence of better vaccinal protection for patients suffered from rheumatoid polyarthritis after 1 month between antipneumococcal vaccination and the initiation of methotrexate. The objective is to compare immunologic response for antipneumococcal vaccination between patients who are vaccinated in the same time of initiation of methotrexate and patients who are vaccinated 1 month before the beginning of the treatment. 