How many (booster) shots do older people really need under Omicron?

Last update: Tuesday 2/15/22 

We begin this note with a brief recap. When Delta became the dominant variant in the U.S. last summer, it was found to be more transmissible, more lethal, and produced more breakthrough infections than previous variants. Our vaccines lost much of their effectiveness in preventing new infections after five or six months, although they remained highly effective in preventing severe illness and death. Our vaccines elicited weaker immune responses among older people and people who had compromised immune systems. Taken together these factors encouraged the distribution of booster shots to people who were older, immunocompromised, or worked on "front-line" jobs that exposed them to greater contact with the disease. As if all of this weren't bad enough, along came Omicron and our winter of discontent.

Here are a few links to news reports that cover the points just made in our recap:

• "Outbreak of SARS-CoV-2 Infections, Including COVID-19 Vaccine Breakthrough Infections, Associated with Large Public Gatherings — Barnstable County, Massachusetts, July 2021", CDC, 7/30/21       
  
  
• "Vaccine Effectiveness Against Infection May Wane, C.D.C. Studies Find", Apoorva Mandavilli, NY Times, 8/18/21
  
  
• "C.D.C. Chief Overrules Agency Panel and Recommends Pfizer-BioNTech Boosters for Workers at Risk", Apoorva Mandavilli and Benjamin Mueller, NY Times, 9/24/21 

Full disclosure ==> The editor/author of this note is way, way beyond 65, so he has a personal interest in full boosting for older folk.

Omicron, the global game changer

Omicron was first detected in South Africa in November 2021 and quickly became the dominant variant everywhere in the world because it was two to three times as transmissible as Delta and could evade vaccines more successfully. Although Omicron was "weaker" than Delta in that it hospitalized a smaller percentage of the people it infected, its far greater transmissibility enabled it to infect far more people thereby causing hospitalizations to strain the capacity limits of most' healthcare systems. The first Omicron case was detected in the U.S. in late November, 2021.

• "Covid Updates: South Africa Identifies New Variant", NY Times, 11/26/21
  
  
• "Classification of Omicron (B.1.1.529): SARS-CoV-2 Variant of Concern",
   World Health Orgsnzation (WHO), 11/26/21 
  
  
• "California has reported the first U.S. case of the omicron variant", Bill Chapell and Jonathan Franklin, NPR, 12/1/21
  
  
• "Prior Infection Is Little Defense Against Virus Variant, Scientists Say", Lynsey Chutel and Richard Pérez-Peña, NY Times, 12/2/21 
  
  
• "Omicron Infections Seem to Be Milder, Three Research Teams Report", Carl Zimmer and Emily Anthes, NY Times, 12/22/21 
  
  
• "Omicron Drives U.S. Virus Cases Past Delta’s Peak", Lauren Leatherby, Charlie Smart and Amy Schoenfeld Walker, NY Times, 12/23/21 
  
  
• "Omicron will infect ‘just about everybody,’ Fauci says", Andrew Jeong and Ellen Francis, Washington Post, 1/12/22 

Booster shots for everyone ... except for those age 65 and older

As per the following link, the CDC's decision to recommend booster shots for everyone preceded Omicron's arrival in the U.S. by a couple of weeks.

• "C.D.C. Endorses Covid Vaccine Booster Shots for All Adults", Apoorva Mandavilli, NY Times, 11/20/21 

Someone (unknown?) suggested the following useful heuristic when discussing vaccinations and boosters under Omicron ==> Omicron seems to remove one level of immunity from everyone.

-- People who only had one shot (of a two-shot vaccine) or who had been infected but recovered now had no immunity when facing Omicron 

-- People who had two shots, now had only one, so they were no longer fully vaccinated

-- People who had two shots and one booster, now had two shots; so they were back to full vaccination under Delta, but this was insufficient to protect them from being infected by the more clever Omicron

All of the above "explains" Dr. Fauci's prediction that sooner or later, everyone will be infected by Omicron.

The reader may recall that older persons and persons who were immunocompromised received booster shots under Delta because their immune systems did not produce a big enough response to two shots. At some point, which the author of this note cannot identify, the CDC changed its official definition of "fully vaccinated" for immunocompromised persons to mean three shots, i.e., the third shot was now officially necessary for full vaccination. The third shot was no longer regarded as a booster. So immunocompromised people became eligible to receive a fourth shot as their booster. Here's a link to a CDC page that states that 

"After completing the primary series, some moderately or severely immunocompromised people should get an additional primary shot. Everyone 12 years and older, including immunocompromised people, should get a booster shot. If you are eligible for an additional primary shot, you should get this dose first before you get a booster shot."

To date, the CDC has not redefined the "primary" doses for older people as including a third injection ... Israel provides four shots to older people (three primary plus one booster), so why doesn't the U.S.? Why are the primary victims of the virus less protected under Omicron?

• Israel, "Israel to Start Giving Fourth Covid Vaccine to People Over 60", Daniel Avis, Bloomberg 1/2/22  

A recent CDC report concluded that older U.S. residents were the only age groups to receive substantial benefits from booster shots under Delta, so it's likely that they will also receive the biggest benefits from boosters under Omicron.

• "Younger Americans Benefited Less From Booster Shots Than Older People", Apoorva Mandavilli,  NY Times, 2/4/22

How long are boosters effective under Omicron? ... And for whom?

Given that the effectiveness of primary doses faded after five or six months under Delta, how many months did boosters last before they faded? Four months, according to a more recent CDC report, under Delta and Omicron:

• "New C.D.C. data adds to evidence that boosters’ protection against severe Covid plunges after four months.", Apoorva Mandavilli, NY Times ... CDC, 2/11/22

A couple of bothersome devils lurk in the details of this report, so some of its principal findings will be quoted verbatim with highlighted comments in the following bullets

• "CDC recommends that all persons aged ≥12 years receive a booster dose of COVID-19 mRNA vaccine ≥5 months after completion of a primary mRNA vaccination series and that immunocompromised persons receive a third primary dose."
  
  
• "A test-negative case-control study design using data from eight VISION Network sites§ examined vaccine effectiveness (VE) against COVID-19 emergency department/urgent care (ED/UC) visits and hospitalizations among U.S. adults aged ≥18 years at various time points after receipt of a second or third vaccine dose during two periods: Delta variant predominance and Omicron variant predominance (i.e., periods when each variant accounted for ≥50% of sequenced isolates)"
  
  -- Comment: Delta period was probably August 26, 2021 through mid-December 2021
  -- Comment: Omicron period was probably mid-December 2021 through January 22, 2022
  
  
• "Persons categorized as having received 3 doses included those who received a third dose in a primary series or a booster dose after a 2 dose primary series (including the reduced-dosage Moderna booster). "
  
  -- Comment: Here's Devil #1. The analysis did not distinguish between 2 primary +  1 booster vs. 3 primary. One would have expected that the third primary (for immunocompromised) would not last as long as a booster (for non-immunocompromised)
  
  
• "The VISION Network analyzed 241,204 ED/UC encounters** and 93,408 hospitalizations across 10 states during August 26, 2021–January 22, 2022."
  
  
• "VE after receipt of both 2 and 3 doses was lower during the Omicron-predominant than during the Delta-predominant period at all time points evaluated."
  
  
• "During both periods, VE after receipt of a third dose was higher than that after a second dose; however, VE waned with increasing time since vaccination."
  
  -- Comment: Once again, booster shots would have been expected to maintain higher vaccine effectiveness (VE) than third primary shots (for immunocompromised). Therefore treating both as "booster" shots would suggest that booster VE waned faster than it really did.
  
  
• "During the Omicron period, VE against ED/UC visits was 87% during the first 2 months after a third dose and decreased to 66% among those vaccinated 4–5 months earlier; VE against hospitalizations was 91% during the first 2 months following a third dose and decreased to 78% ≥4 months after a third dose."
  
  -- Comment:  Treating third primaries as "booster" shots would underestimate the effectiveness or real boosters in keeping moderate cases out of emergency rooms and urgent care  ... and overestimate the effectiveness of third primary shots in keeping severe cases out of the hospital. Immunocompromised persons with three primary shots, i..e., no booster, are more likely to be hospitalized than if they had a real booster, i.e., a fourth shot.
  
  
• "For both Delta- and Omicron-predominant periods, VE was generally higher for protection against hospitalizations than against ED/UC visits."
  
  -- Comment: No surprise here. Primary shots and boosters were primarily designed to reduce severe illness (hospitalizations); they were not designed to reduce infections or moderate illness (emergency rooms/urgent care)

Finally, here's Devil #2, the devil dog that didn't bark ... because it wasn't there. The report did not analyze the waning of VE by age groups. Specifically, it did not check to see how long the effectiveness of 3rd shots lasted for the oldest, most vulnerable age groups. Perhaps the effectiveness against hospitalization for the oldest declined far below the overall decline to 78 percent ... :-(

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Links to related notes on this blog:  

• "Returning to normal living by leveraging the background immunity of local communities", Last update: 2/12/22