Lyme disease vaccine shows strong results. How it works.

Pfizer and Valenva are seeking regulatory approval from the Food and Drug Administration for a Lyme disease vaccine in development that's more than 70% effective against the tick-borne illness. Although fewer-than-expected cases in the study made it difficult to assess the vaccine's effectiveness on a large scale.

When compared to a placebo, the vaccine showed a 73.2% efficacy rate against confirmed Lyme disease cases beginning 28 days following the fourth dosage.

Pfizer is more confident "in the vaccine's potential" as it prepares "submissions to regulatory authorities" after a second planned analysis, the company said in a recent statement.

The Centers for Disease Control and Prevention said Lyme is the most common disease transmitted through tick bites. Currently, there are no approved vaccines available that prevent Lyme disease, which is spread by the blacklegged tick and Western blacklegged tick, commonly known as deer ticks. The CDC estimates that roughly 476,000 Americans are diagnosed with the illness each year.

Unable to view our graphics? Click here to reload.

How the Lyme disease vaccine works

The Lyme disease-causing bacteria's outer surface, known as OspA protein, is the focus of the company's vaccine. The shot produces protective antibodies that are transmitted to the tick upon biting a vaccinated person, preventing the bacteria from spreading from tick to human host. The first year of the series consists of three shots, followed by a booster shot the next year. Here's how it works:

Is Lyme disease curable?

The hallmark symptoms of Lyme disease in the acute stage include a “bullseye” rash (erythema migrans), fever, chills, fatigue and muscle and joint aches. Without treatment, Lyme disease can progress to include neurological, heart and joint problems. 

Lyme disease can be curable, especially if it is treated early with a suitable course of antibiotics lasting two to four weeks. Most patients recover completely from this condition. Although the Borrelia burgdorferi infection is typically eradicated by quick treatment, some individuals have persistent symptoms, which are referred to as Post-Treatment Lyme Disease Syndrome, according to the CDC.

Where is Lyme disease most common in the US?

With rising temperatures due to climate change, tick populations have expanded into new regions and exposed more people to ticks and their illness-causing bacteria. Annual cases are expected to continue to climb.

In high-risk areas, an estimated 10% to 50% of blacklegged ticks carry the bacteria that cause Lyme disease. These high-risk areas include:

• Eastern states, primarily New England and the mid-Atlantic.
• The Great Lakes Region and northern Midwestern states, especially Wisconsin and Minnesota
• The West Coast, particularly parts of northern California and, less commonly, Oregon and Washington

How to stay safe from tick bites

The CDC and other public health authorities recommend the following to keep you and your family safe from ticks:

• When spending significant time outdoors, treat clothing and gear with products that have .5% permethrin or buy such items already pre-treated with permethrin.
• Consider long pants and high socks instead of shorts.
• Avoid high grass and leaf litter. On hikes, try to walk in the center of trails.
• Inspect clothing and gear periodically for the presence of ticks.
• To learn how to properly remove a tick if it's attached to skin, click here.

SOURCE Pfizer, Centers for Disease Control and Prevention, Johns Hopkins and USA TODAY research

This story was updated to add new information.