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Home » COVID vaccine booster effectiveness may wane quickly against Omicron

COVID vaccine booster effectiveness may wane quickly against Omicron

This pandemic just doesn’t give us much good news — research from the UK indicates that COVID-19 vaccine booster effectiveness may wane significantly at the 10-week mark post-vaccination. This may allow the Omicron variant to spread much further than originally hoped.

Before I explain the research, I want to make a few things very clear. First, this doesn’t mean the vaccine is ineffective, it is just that the immunity appears to wane more quickly than other vaccines. Second, this doesn’t mean that the vaccines are worthless — hospitalization and, more importantly, death rates are much lower in the vaccinated group. And finally, this is how science works — we accumulate data and then, after reviewing the data, change recommendations.

Let’s take a look at this new research and determine what it may mean for future vaccination efforts.

woman giving vaccine to a man
Photo by Nataliya Vaitkevich on

Research on COVID-19 vaccine booster effectiveness

In a technical briefing from the UK Health Security Agency, researchers found that the vaccine effectiveness against symptomatic infection generally fell to around 40% after about 2.5 months after the booster date. The agency assessed 147,597 Delta variant cases and 68,489 Omicron variant cases between November 27 through December 17.

COVID-19 vaccine booster effectiveness, Pfizer
Pfizer vaccine effectiveness against Delta and Omicron variants

The research showed the drop in the Pfizer vaccine effectiveness at 10 weeks against the Omicron variant to nearly 0 after two doses and about 45% after a Pfizer booster. Interestingly, after a Moderna booster, the effectiveness remains close to 80%. Furthermore, the Pfizer vaccine showed excellent effectiveness against the Delta variant.

COVID-19 vaccine booster effectiveness, AstraZeneca
AstraZeneca vaccine effectiveness against Delta and Omicron variants

For the AstraZeneca vaccine, effectiveness peaked at 60% two to four weeks after a Pfizer or Moderna booster but fell to 35% with Pfizer and 45% with Moderna by 10 weeks. AstraZeneca uses the adenovirus vector as opposed to the mRNA used by Pfizer and Moderna. This may indicate that the mRNA vaccines have stronger effectiveness, but we will need more data.

COVID-19 vaccine booster effectiveness, Moderna
Moderna vaccine effectiveness against Omicron and Delta variants

The researchers were not able to determine booster effectiveness for the Moderna vaccine because of low numbers in the UK. However, after two doses, the effectiveness is 0% after about 20-24 weeks after the second dose.

This report did not include data on vaccine effectiveness against severe disease, including hospitalization and death, because the number of Omicron cases admitted to the hospital following a positive test was too small to create an estimate.

This data supports data from Israel that suggested that there was waning effectiveness after a booster dose of the Pfizer vaccine. It appears that there is a doubling in the rate of infection with the Delta variant among individuals ages 60 and above within four to five months of the third shot. This has led the Israeli government to recommend a second booster dose given at least four months after the first booster for a total of four doses.

Peter Hotez, MD, Ph.D., of Baylor College of Medicine in Houston, has been pushing for a fourth dose of the Moderna and Pfizer vaccines because of the Omicron variant. He wrote in a Los Angeles Times article:

We must take quick action to prevent instability in our health system. If there are data to support its safety and impact, an emergency fourth shot might be offered to those healthcare workers now several months out from their booster shot. Doing so could reduce the risk of breakthrough symptomatic infection and keep these individuals on the job.

man in red crew neck sweatshirt photography
Photo by Andrea Piacquadio on

Some good news in the report

The report showed that there was about a 60% reduced risk of hospitalization with Omicron compared with Delta. The matches with data that have been reported.

In fact, another report from the UK Health Security agency put infection severity of the Omicron variant in the lowest-risk “green” category based on these findings and three other analyses:


This report has some bad news about the vaccine effectiveness, implying that we may need to rework the vaccine or add more boosters to deal with the Omicron variant. However, we don’t know if the effectiveness against hospitalization and death from Omicron remains high or has dropped. That will take more time.

This does not mean that the vaccine is worthless. It still protects against the more dangerous Delta variant and may reduce the risk of hospitalization and death from the Omicron variant.

I know that anti-vaxxers will use this data as another reason to dismiss the vaccines, but nothing could be farther from the data and evidence that continues to support the safety and effectiveness of the COVID-19 vaccines.

Michael Simpson

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