Coronavirus: Pfizer's Vaccine Effectiveness in Rapid Decline Over Time?

Are we seeing a rapid decline over time regarding the effectiveness of the Pfizer COVID-19 vaccine?

CNBC (Jul 23) has an article about a study coming out from Israel:

Pfizer and BioNTech’s Covid-19 vaccine is just 39% effective in Israel where the delta variant is the dominant strain, but still provides strong protection against severe illness and hospitalization, according to a new report from the country’s Health Ministry.

The efficacy figure, which is based on an unspecified number of people between June 20 and July 17, is down from an earlier estimate of 64% two weeks ago and conflicts with data out of the U.K. that found the shot was 88% effective against symptomatic disease caused by the variant.

However, the two-dose vaccine still works very well in preventing people from getting seriously sick, demonstrating 88% effectiveness against hospitalization and 91% effectiveness against severe illness, according to the Israeli data published Thursday.

Here are some raw data points that I think are important:

First, per Worldometer, Israel's 7 day moving average is coming in at around 1,100 cases per day and is trending upwards. It is still much lower than the previous two significant waves that hit around 6,200 in September-October 2020 and around 8,300 in December 2020-February 2021. But once again, I'm comparing the height of the last two significant waves versus one that is still heading upwards.

Second, per Our World in Data, a little over 61% of Israel's population is fully vaccinated.
Now the UK also released a study that showed Pfizer's vaccine was 88% effective against the delta variant. Hmm.

The Jerusalem Post (Jul 24) dug into why these studies differ so much:

1. Israel's study indicated that the vaccine was only 40% effective against symptomatic symptoms.

2. Israel's study indicated it is 91% effective against serious outcomes and 88% effective against hospitalization.

3. The UK study indicated 88% effectiveness against symptomatic infection.

 
Okay, to me, the comparison is Israel's 40% vs the UK's 88% as the article mentions that these are the percentages against symptomatic symptoms. That is a rather wide gap.

4. These two data points might actually indicate that Pfizer's vaccine is less effective over time. Per Our World in Data, Israel was at 50% vaccination by March 16. It took the UK until July 6th to reach 50%. We might want to see another UK study three and a half months from now to see how it aligns with the current study from Israel.

5. Age might play a factor. Israel used Pfizer for all age groups while the UK used Pfizer for those under 40. So maybe the vaccine works better for those who are younger?

As of yet, I am not aware of any similar studies from the Untied States. Of course, the United States is just a touch below 50%. The New York Times (Jul 23) had this to say; however, from Dr. Anthony Fauci:

Dr. Anthony S. Fauci, who heads the infectious disease division of the National Institutes of Health, said he was surprised by the apparent steep falloff in the Pfizer vaccine’s effectiveness that the Israeli data seems to suggest. He said he wanted to compare it with data that the C.D.C. had been gathering from cohorts of thousands of people across the United States. “People are sort of raising their eyebrows a bit,” he said.

So the United States government is definitely paying attention to these studies and also starting up their own studies.