We're getting closer to an effective COVID-19 vaccine. Here's what it will cost to get a shot.

• The US is getting closer to having an effective COVID-19 vaccine, after drug company Pfizer said Monday that its experimental vaccine is 90% effective at preventing the disease caused by coronavirus.
• A vaccine won't be effective if most people don't take it, and that will depend on whether people can afford it.
• The US government has already agreed to buy hundreds of millions of doses of future COVID-19 vaccines from drugmakers. President-elect Joe Biden has also said he will guarantee free vaccines to every American.
• Congress in March called on COVID-19 vaccines to be free for all Americans. Federal regulation in recent weeks has implemented that legislation and requires Medicare, Medicaid and private insurers to cover the vaccine at no cost to members.
• A relief fund for healthcare providers will help to cover the cost of the vaccine for people who don't have insurance.

The US just got much closer to having an effective vaccine to battle the COVID-19 pandemic, after drug company Pfizer said Monday that its experimental coronavirus vaccine proved 90% effective at preventing the disease.

But a vaccine won't work unless most people take it, and that will hinge largely on whether people can afford it. The federal government has taken steps in recent weeks to ensure that many Americans will be able to get the vaccine for free.

Congress passed legislation in March that called for free COVID-19 vaccines for all Americans. In October, the Centers for Medicare and Medicaid Services said Medicare, Medicaid and most private health insurers will be required to provide the vaccines at no cost to their members. The US government will pay for those vaccines.

As part of Operation Warp Speed, the government has already agreed to buy hundreds of millions of COVID-19 vaccines from drug companies. In July, the government reached a deal with Pfizer to buy 100 million doses for $1.95 billion, and included an option to buy up to 500 million more doses.

President-elect Joe Biden has also said he wants the COVID vaccine to be available for free. He will invest $25 million into a vaccine manufacturing and distribution plan that guarantee free vaccines to every American, according to his plan.

A COVID-19 vaccine will likely be free for most insured people

Medicare, which covers about 62 million people, will cover a future vaccine that receives a greenlight from the U.S. Food and Drug Administration, either through an emergency use authorization or licensed under a Biologics License Application, CMS said in an interim final rule released in October.

Seniors and other people covered by Medicare won't have to pay any cost-sharing, including deductibles or coinsurance, which is the percentage of cost people must pay after meeting a deductible, according to the rule. Medicaid programs, which cover 76.5 million people, are also required to cover the cost of the vaccine through the public health emergency.

People with private health insurance through their jobs or the individual market also will be able to get a vaccine for free. About 157 million people receive coverage through their employers.

The ACA requires most insurers and employers to cover preventive services, including vaccines, at no cost to the member. But that doesn't mean all vaccines.

The Advisory Committee on Immunization Practices that's a part of the Centers for Disease Control and Prevention has to sign off on it, Sabrina Corlette, a Georgetown University research professor and expert on private insurance, told Business Insider.

"If you are in health coverage that is covered by the Affordable Care Act—and that's a caveat because we know there are lots of people who may be in plans not subject to the ACA, like short-term plans—and a vaccine is recommended by this committee, health plans within 15 days have to cover it and they can't charge you a deductible or coinsurance or copayment for that vaccine," Corlette said.

Usually, health insurers have up to two years after ACIP recommends a vaccine before they have to begin covering a vaccine. The March legislation, known as the CARES Act, sped up that timeline by requiring insurers to cover COVID-19 vaccines 15 days of the committee's recommendation.

The cost of administering vaccines should be covered as well

The CMS interim final rule in October went a step further to require health plans and insurers to cover both the COVID-19 vaccine and the administration of that vaccine for free, even if it is given by an out-of-network doctor. Those rules are effective immediately and last for as long as the public health emergency.

When asked if it would cover a COVID-19 vaccine for free, large health insurer Aetna, which is owned by CVS Health, said it would provide the vaccine without cost-sharing for its members, consistent with the CARES Act and recent federal regulation. Other major health insurers did not respond by deadline.

As for people who don't have insurance, the government will use the Cares Act Provider Relief Fund, which was established to help providers weather the pandemic, to cover their costs.