Why One Dose of a Two-Dose Vaccine Is Not Enough

When you receive your first dose of two-dose vaccine COVID-19 (in other words, of Pfizer vaccine or Moderna), evidence suggests that your defense begins in about two weeks – before you get a second dose. This is good news, but that doesn’t mean you can skip your second dose.

The latest study confirming this graph came out this week, showing that the medical and key workers involved in the study were 80% protected two weeks after the first dose, and the effectiveness increased to 90% two weeks after the second dose.

Other studies in the past few months have shown similar results. In one study in Israel , the first dose of Pfizer vaccine was 46% more effective at preventing infections between days 14 and 20, even more effective if you are looking at symptoms, hospitalization, or serious illness than just positive tests. on COVID. … However, one week after the second dose, the effectiveness against infection reached 92%.

Business Insider compiled several studies here and found that Pfizer and Moderna vaccines appear to be 80% effective after the first dose. But it’s important to note that these studies ask the question of what happens between two doses, rather than whether you can get just one.

Clinical trials have not tested what happens when you skip or delay a second dose.

Despite the lack of evidence, Canadian scientists argue that the first dose provides sufficient protection, so the second dose should be delayed until 12 weeks instead of 3-4 weeks. Others argued that the 12-week delay has never been tested in clinical trials, so we don’t know if greater spacing between shots will lead to the same effectiveness in the long run.

Oddly enough, I heard people pondering if they could skip the second dose at all. Since the immune response often increases after a second dose, this might seem like an attractive proposition. But then again: we don’t know if a single dose of a two-dose vaccine actually works, so the expert advice remains firm: get both doses .

“I can’t stress enough how important it is to get a second dose, ” an infectious disease specialist told Yahoo! Life .

“If you don’t get a second shot, you’re not fully protected and you’re not protecting others at the same time, ” said the South Carolina Deputy Public Health Officer , noting an increase in the number of residents missing a second dose.

“Get the vaccine when it’s available to you and make sure you don’t miss a second dose, ” wrote an infectious disease specialist on the Ohio State University website . He points out that animal trials were to compare one dose to a two-dose regimen, and that a double dose became the standard because it was more effective.

So if you got the first dose of the two-dose vaccine, experts agree that you should get the second. If for some reason the number of doses is important to you, it may be helpful to know that Johnson & Johnson’s vaccine only requires one dose. But experts agree that all three vaccines available in the US are safe and effective, and you should get everything you can.


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