The series of medical leaves that Steve Jobs took before he finally resigned last month seem to have had an inoculating effect on both investors and consumers, allaying their concerns about Apple’s (AAPL) future without its co-founder and CEO.

The effect on investors was apparent three weeks ago, when Apple’s shares rose in the days after Jobs’ resignation.

Evidence of the effect on consumers comes from a survey of 2,297 ChangeWave members conducted between Sept. 6 and Sept. 12.

Asked about their interest in buying the company’s products, now that Jobs has stepped down, 4% said they would be less likely to buy from Apple in the future, and 89% said his resignation would have no effect.

When asked a similar question in June 2008, 18% of respondents — nearly one in five — said they would be less likely to buy Apple’s computers and handheld devices if Jobs were no longer able to run the company.

ChangeWave, a division of the 451 group, has put this question to its members seven times over the past three years. As the chart above shows, the impact of Jobs’ stepping down has diminished significantly.

In the September survey, 1% said they were more likely to buy Apple products now, and 6% didn’t know how they felt.

The full ChangeWave report — with more detail on consumer demand for and satisfaction with the iPad — is available here.