Usually the element following proposed as functions as a noun phrase. The Oxford Learner's Dictionary of Academic English provides an example under "propose verb":
to suggest a plan or an idea for people to consider and decide on
propose something as something Remote Internet voting has been proposed as a solution to the problem of low voter turnout.
This suggests that the participle form providing in your example is functioning like a noun phrase. This is a common definition of a gerund - a present participle / -ing form verb that functions as a noun. (See this ThoughtCo article for a fair summary.) The gerund heads a clause explaining what is being proposed.
"Why is it there?" is a fair question, since a punctilious editor might point out that the sentence works fine grammatically without the gerund:
In this context, gene drives have been proposed as a new means of tackling a disease that still infects 200 million people and causes half a million deaths each year.
That said, the construction still works and may serve a semantic or emphatic purpose. Provide as a verb frequently takes as its object what is being given or made available (See the OLD entry for examples). Using providing also avoids issues if gene drives are not actually the new means but are only used to engineer or develop (or provide) the new means. So the gerund providing emphasizes that, if the proposals are accurate, gene drives would *provide a new means" for solving a problem.