US CDC recommends third vaccine dose in some groups

Simon Collins, HIV i-Base

At a meeting on 22 July 2021 of the US Advisory Committee on Immunization Practices (ACIP), a presentation from the US CDC recommended a third dose for some people who are immunocompromised. [1]

An excellent slide set compiling the available evidence is also available online. [2]

Based on 2013 data, the CDC estimates this group to be approximately 2.7% of the US adult population (roughly 5 to 6 million people).

This includes:

  • Solid tumour and hematologic malignancies.
  • Receipt of solid-organ or hematopoietic stem cell transplant.
  • Severe primary immunodeficiencies.
  • People living with HIV.
  • Treatment with immunosuppressive medications. These include cancer drugs, TNF blockers, certain biologic agents (eg rituximab), and high-dose corticosteroids.

This is not proposing a third dose to the whole population.

Currently, many people who have received two doses assume protection when this might not be the case. These people are more likely to have breakthrough infections.

  • 44% of hospitalised breakthrough cases in the US are immunocompromised people.
  • 40% of hospitalised breakthrough cases in Israel are immunocompromised people.

The recommendations are similar to earlier guidelines in France, Israel and the UK. [3, 4, 5]

The US FDA with also apparently need to either approval this off-label use or approve the third vaccine.

Pfizer announced plans to apply for an indication for three doses in July 2021. [6]


  1. ACIP meeting (22 July 2021).
  2. Oliver S. Data and clinical considerations for additional doses in immunocompromised people. (slides page) (PDF slides)
  3. France routinely recommends third dose of COVID-19 vaccine for some people with reduced immune function. HTB (1 June 2021).
  4. CNBC. Israel is offering a third Pfizer shot amid spiking cases, even as the U.S. says it’s not yet needed. (13 July 2021)
  5. Plans for universal third vaccine dose for UK adults from September. HTB (1 July 2021).
  6. STAT news. Pfizer to seek FDA authorization for third, booster dose of its Covid-19 vaccine. (8 July 2021).

This report was frist published on 26 July 2021.

Links to other websites are current at date of posting but not maintained.