Your Second Vaccine Dose Is Crucial

Don’t skip your second Pfizer or Moderna shot. Without it, your protection won’t be as strong or long-lasting.

Photo: Mick Haupt via Unsplash

Almost 150 million doses of Covid vaccine have been administered in the United States. Most adults are now at least partially vaccinated, and more and more people are choosing to get vaccinated every day. But some people may be wondering if their second shot is necessary. The answer is yes.

If you got one dose of an mRNA vaccine (Pfizer or Moderna), don’t skip the second dose. Without it, your vaccine-induced protection won’t be as strong or long-lasting. The second dose greatly reinforces the protection your immune system started building after the first shot.

With new variants in the mix that are more contagious and likely deadlier, being fully vaccinated is even more essential. Although the vast majority of people who start vaccination get both doses, 8% of people who have received their first dose hadn’t yet received their second, according to data released by the Centers for Disease Control and Prevention (CDC).

Some people may fear the side effects of the second dose, which could be stronger than the first. Others may have had to cancel their second appointment or experienced difficulties scheduling it. A few have an intense fear of needles. And a portion of the population is misinformed, believing that the one dose of vaccine provides enough protection. (It doesn’t if you’re getting Pfizer or Moderna’s vaccines.)

In an important real-world study, CDC found that mRNA vaccines were 80% effective after the first dose, and 90% effective after the second. Although 80% effective seems good on the surface, some studies have found a lower effectiveness after only one dose and others suggest that coronavirus antibodies don’t peak until after your second dose. Currently, it’s clear that protection lasts at least six months, and probably more when you’re fully vaccinated. But we don’t know how durable or long-lasting the protection is from just one dose.

Even if you’ve already had Covid, evidence shows the vaccine boosts your antibodies. The “natural immunity” you gain after recovering from a Covid infection is good, but vaccination is super-human. Getting vaccinated reinforces the protection your immune system has already built and reduces the risk that you’ll get reinfected.

The CDC provides guidelines on which Covid vaccines require two doses, the timing for the second shot, and when you’re considered fully vaccinated.

There’s been a lot of focus on herd immunity—when enough people within a population are protected against a disease, either through vaccination or natural infection. It’s important to think of herd immunity more as a dimmer dial rather than an on-off switch. Bottom line: The more of us who get vaccinated, the safer we all are.

To stop the spread of the coronavirus and save thousands of lives, we must get fully vaccinated. Don’t let your guard down too early. It takes two weeks after the first dose for your immune system to begin building protection, and if it’s been less than two weeks since your second dose, or if you’ve only had one dose of a two-dose vaccine, you’re not fully vaccinated.

In the United States, we’re making significant progress against Covid and we’re closer than ever to resuming life as usual. New CDC modeling shows that if we keep up our vaccination pace and continue to mask and distance for the next couple of months, we’ll be able to get to the new normal. Our challenge now is to reach those as yet unreached with vaccines by making it as convenient as possible for everyone to get vaccinated and continue to fight the fatigue many of us feel with masking, social distancing, and other protection protocols. By summer, we’ll be in much better shape, and by the fall, at the new normal in the United States.

The federal government just rolled out, a new website where you can find where to get Covid vaccine near you. Check it out and schedule an appointment to get vaccinated as soon as you can!



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Dr. Tom Frieden

Dr. Tom Frieden


President and CEO, Resolve to Save Lives | Former CDC Director and NYC Health Commissioner | Focused on saving lives.