p Dr. Dennis Y. Fong, M.D.
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Covid Advice #16 (09/25/2021):
Booster Update, Delta, Keep Your Mask On and Your Guard Up

- from Dr. Dennis Fong -


In line with the latest FDA ruling, the CDC has just released its booster recommendation yesterday. As you may remember, the booster statement the CDC sent out on August 18 recommended boosters at 8 months for all persons who have had either Pfizer or Moderna vaccines, but that is no longer in yesterday's CDC recommendation. You can find the recommendation here: CDC booster recommendation.

The CDC now recommends boosters for:

  1. The Pfizer vaccine only,
  2. After "at least 6 months" of the second shot,
  3. For persons 65 and older, younger persons with underlying medical conditions, and health care workers and others in high Covid risk occupational or institutional settings.

So for those of you who got the Pfizer vaccine, you can go ahead and get a booster as soon as 6 months after your second shot. for example, if you had your second shot in February or March, then you can get your booster now; if April, then in October, and so forth.

For those of you who got the Moderna vaccine or the Jansen (Johnson & Johnson) vaccine, you will have to wait for a ruling by the FDA.

Again, I think the booster is a good idea.


Delta has changed the equation -- again, I think it's wrong to think that just because you have been vaccinated, you can let down your guard.

First, vaccine effectiveness is significantly lower against Delta than against the original Covid. Against the original Covid, both Moderna and Pfizer were 90% plus effective. In July, however, the Israel Health Ministry released data showing that Pfizer was only 39% effective against Delta. And Israel has had more experience with Pfizer against Delta than any other nation: Pfizer is the only vaccine they've ever had, and Delta has gotten to Israel signficantly sooner than to US. See report here: Israel on Pfizer effectiveness against Delta. Also, a recent study of 25,000 plus Mayo Clinic patients showed that in July, when Delta was 70% of the Covid infections, Moderna was 76% protective while Pfizer was only 42% effective. See the study here: Comparing 2 mRNA Vaccines. And there's a lot more Delta now, about 100%, than when the study was done in July, only 70%.

(By the way, for those of you who got the Moderna vaccine but can't get the booster yet like those who got Pfizer now can, it may be comforting to know that the Moderna vaccine seems to be signficantly more effective against Delta than the Pfizer.)

Second, there's a lot more Covid around now than last year, and the more Covid there is, the more chance of breakthrough infections. For the first 3 weeks of this September, in 2021, the average number of cases per day in the US has been 156,000 plus. So this September the US daily cases has been 4 times as many as back last September. Our Contra Costa County has actually not been performing very well: while the number of cases per 1,000 persons this August for the whole of California has been half of that of the US national average, the number in Contra Costa has been almost the same as national average; that is, in August Contra Costa has been twice as high as California state average. With this much Covid and we are only in September, this winter should be much worse than last winter.

So keep your mask on and your guard up, even if vaccinated. You don't want to get infected, because while vaccines do protect you a lot against both serious Covid and long Covid, it's not 100%.

Wish you happiness! Stay healthy and stay safe!

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