Céline Gounder, an internist, infectious-disease specialist and epidemiologist, is host of the “Epidemic” and “American Diagnosis” podcasts, chief executive of Just Human Productions and a CNN medical analyst. She served on the Biden-Harris Transition Covid-19 Advisory Board.

Michigan Gov. Gretchen Whitmer, a Democrat, is calling on the Biden administration to surge covid-19 vaccines to her state, where overall cases are as high as they were in November thanks in part to the B.1.1.7 variant of the virus first identified in Britain.

I feel for the governor, but vaccines are not going to save her state. The best strategy for Michigan at this point is to implement the same public health measures that we’ve been using for more than a year.

This is an important lesson not only for Michigan, but also in other places experiencing a surge. The B.1.1.7 variant, now the dominant strain of covid-19 in the United States, is wreaking havoc in Michigan and Minnesota. It’s driving an increase in cases in the Northeast, Mid-Atlantic, Florida and parts of Texas. B.1.1.7 is landing even younger adults in the hospital with severe covid-19. The Michigan Health and Hospital Association found that hospitalizations increased by 633 percent among adults in their 30s and by 800 percent for adults in their 40s over the course of March.

So why not just send more vaccines to Michigan? Well, first, because the state already has enough vaccine supply. Michigan is one of several states with rural populations that has vaccination appointment slots going unfilled.

Plus, the Federal Emergency Management Agency deployed staff in February to assist Michigan with vaccine distribution and administration logistics. And now, the Biden administration is sending 160 more federal staff to supplement 230 already supporting covid-19 operations in the state. More testing capacity and therapeutics are also on the way.

There’s another, more important reason for why more vaccines won’t stop the surge: the coronavirus’s incubation period. Some have suggested we adopt “ring vaccination,” a strategy used to eradicate smallpox in which everyone who has been exposed in an outbreak is vaccinated. But covid-19 isn’t smallpox. Covid-19 has a median incubation period of four to five days; smallpox, 10 to 14 days. It takes about 14 days after one dose of smallpox vaccine for someone to develop an immune response. This means that smallpox vaccination can prevent illness even after someone’s been exposed. Covid math isn’t smallpox math.

It’s important to remember that it takes time for your immune system to recognize a vaccine and mount an immune response to it. You aren’t immune the second the needle hits your arm. It takes 14 days after two doses of Pfizer and Moderna vaccine and 14 to 28 days after a dose of Johnson & Johnson vaccine to be “fully immunized.” So even if a large proportion of Michigan residents were to be vaccinated today in the middle of the state’s surge, the impact of vaccine-induced immunity wouldn’t be seen until at least a month from now. Vaccinating today won’t help the people being infected right now.

The hard truth is that the measures that will help curb Michigan’s surge are those that take effect instantly: masking, sticking to household bubbles, socializing outdoors, not gathering indoors and maximizing indoor ventilation. These are the same mitigation measures that we’ve been recommending for months, the same measures we’re all tired of following and the same measures that so many are discarding now that we have vaccines (even if they haven’t yet been vaccinated).

This is likely to be unwelcome news for Whitmer, who has been resisting imposing unpopular pandemic restrictions once again in her state. But it’s important to understand that while vaccines are great at preventing outbreaks from taking off, they are not so great at slowing a surge once it’s happening. I liken the pandemic to a car. Lifting mitigation measures too soon is like taking your foot off the brake before putting the car into park. Meanwhile, more infectious variants such as B.1.1.7 are hitting the gas. And vaccination is like a parking brake: It works well once a car is stopped, but not nearly as well when you’re racing down a highway.

Eventually, as more and more of the population is vaccinated, there will be protection against transmission and a future surge. Until then, governors must act to keep variants from spreading out of control.

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