What are some examples of topic sentences about swine flu?

Swine flu is a very large topic, which is both good and bad when writing a research paper. It's good because it's broad, and you can take a lot of different angles with it. It's bad for the same reason: it can be difficult to narrow the topic down to a manageable amount. 

The purpose of a topic sentence is to introduce and summarize the focus of a paragraph in an essay. This is how a topic sentence differs from a thesis statement, though they, in essence, do the same job. A thesis statement gives an (often arguable) overview of your topic and sets up the essay for the reader, whereas a topic sentence is limited to the paragraph it begins. 

Since you specified a research paper, which is informational (rather than persuasive), I'll assume that you are planning to write about swine flu itself, rather than, for example, taking a social or political angle. To begin to think about what your topic sentences might be, start by writing down what you already know about the topic and see if that sparks some ideas about the main ideas of your paragraphs. For example, one thing you might know about swine flu is that it's transmittable through human contact or through indirect contact like touching a contaminated surface. You may decide that one of your topic sentences should be related to transmission. 

You can also write down questions you have about the topic. Just because you don't know the answer doesn't mean you can't use it; it's a research paper, after all, and it's likely you'll discover the answers as you go along. You may wonder how swine flu differs from the regular flu. A topic sentence could be to compare (or contrast) swine flu and the regular flu. 

Don't get overly concerned about the complexity of your topic sentences, especially since you're still in the beginning stages of your writing process. It's enough to write, for example, "Swine flu is very similar to the regular flu, with only minor differences." You may discover through your research that they are more different than you originally thought, and that's okay! Writing is an ongoing, back-and-forth process. 

For the six sentences you need for your assignment, think about elements like symptoms, diagnosis, history (where the illness originated), medications, etc. There are lots of aspects you can address. Remember, too, that you don't need to address everything there is to know about swine flu. It's better for you to limit your scope and talk about fewer things more in depth than to try to take on too much and give only surface information about lots of elements.