Health Advice



Q&A: Can you skip the second dose of your COVID-19 vaccine?

Lisa M. Krieger, The Mercury News on

Published in Health & Fitness

You dread the prospect of aches and pains. That trip to the clinic is inconvenient and takes time. And that first dose already offers some protection.

Tempted to skip that second dose of your COVID-19 vaccine? Don't do it, experts say. Here's why.

Q: Why do we need two doses?

A: A single dose of Pfizer's or Moderna's vaccine was 80% effective in preventing infections, according to the CDC's March 29 Morbidity and Mortality Weekly Report. The vaccines' effectiveness jumped to 90% two weeks after the second dose.

The second dose is an insurance policy.

In the short term, one dose is probably going to be fine. The reason for a second dose is that you'll have a more durable response.


— Peter Chin-Hong, M.D., infectious disease physician and Associate Dean for Regional Campuses, UCSF

Q: What is the second dose doing that improves upon the first?

A: The purpose of the second dose is to train your immune system to respond to this virus more vigorously.

I'll draw a very simple analogy. If you wish to become an expert in whatever field — let's say, playing the piano — it's not enough just to have one lesson. If you have many lessons, you become much more of an expert.


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