COVID-19 Research Scan (November 4)

Research Scan: November 4, 2021


  • On October 29, the FDA granted emergency use authorization to the Pfizer-BioNTech COVID-19 vaccine for use in children 5-11 years of age.
    • On November 2, following a meeting of the CDC's Advisory Committee on Immunization Practices (ACIP), the CDC recommended the use of the Pfizer-BioNTech COVID-19 vaccine for all 5-11-year-olds.
    • Clinical trials found that a lower dose (10 μg vs 30 μg in those 12+) produced comparable immune responses and was 90.7% effective at preventing laboratory-confirmed symptomatic COVID-19.
  • Health Canada is currently reviewing the Pfizer-BioNTech application to authorize its COVID-19 vaccine for use in children 5-11 years of age.


NACI releases guidance for third doses

  • On October 29, NACI released interim guidance on COVID-19 booster shots. The guidance recommends that populations at highest risk of waning protection following their primary series and at highest risk of severe COVID-19 illness should be offered a booster dose of an mRNA COVID-19 vaccine at least 6 months after completing their primary series. These populations may include:
    • Adults 70 years of age and older;
    • People who received two doses of the AstraZeneca Vaxzevria/COVISHIELD or one dose of the Janssen vaccine;
    • Adults in or from First Nations, Inuit, and Métis communities; and
    • Frontline healthcare workers who have direct in-person contact with patients and who were vaccinated with a very short interval.

Third dose of Pfizer vaccine offers greater protection

  • A large Israeli study looking at the impact of third doses, found that a third dose of the Pfizer COVID-19 vaccine dose led to an 85% reduction in the incidence of COVID-19-related admission to hospital, a 76% reduction in severe disease, and 94% reduction in COVID-19-related deaths (Barda et al., Lancet).
    • A total of 728,321 Israelis aged 12 or above who had received the third Pfizer dose were matched for age, sex, and sociodemographic and clinical characteristics to people people who had received only the two-dose series at least 5 months before.

Most people with severe allergic reactions able to complete 2 dose COVID-19 vaccine series

  • A US study involving 52,998 health care workers looked at self-reported history of high-risk allergy and self-reported allergic reactions after mRNA COVID-19 vaccination. Only 140 (0.3%) health care workers self-reported severe allergic reactions, 6 of whom had a history of high-risk allergy. High-risk allergy history was associated with a 5-fold higher risk of severe allergic reactions after mRNA COVID-19 vaccination (Li et al., JAMA Network Open).
    • Most of the reported allergy symptoms did not impede the completion of the 2-dose mRNA COVID-19 vaccine series.
    • A total of 51,706 (97.6%) received 2 doses of an mRNA COVID-19 vaccine and 474 (0.9%) reported a history of high-risk allergy, 217 of whom included a severe allergic reaction to an injectable medication or vaccine.

Vaccination reduces risk of infection, but breakthrough Delta cases efficiently transmit infection in household settings

  • A UK study looked at community SARS-CoV-2 transmission and viral loads among 162 confirmed Delta COVID-19 index patients and 231 exposed vaccinated and unvaccinated household contacts from September 13, 2020 to September 15, 2021. The secondary attack rate, or the percentage of contacts infected by the index patient, was 25% for fully vaccinated contacts compared with 38% in unvaccinated contacts. The secondary attack rate for household contacts exposed to a vaccinated index patient was comparable to that of household contacts exposed to an unvaccinated index patient (23% for vaccinated vs 25% for unvaccinated).  (Singanayagam et al., Lancet Infect Dis)
    • Although peak viral load (a proxy for infectiousness) of index patients did not differ by vaccination status, viral load declined faster in fully vaccinated index patients.


UK lists Delta sublineage AY.4.2 as variant under investigation

  • On October 22, the UK Health Security Agency released a technical briefing listing a sublineage of the Delta variant, named AY.4.2., as a variant under investigation. AY.4.2 has two additional mutations and appears slightly more transmissible with an estimated 17% growth rate advantage over Delta.
  • The variant first appeared in July 2021 and now accounts for about 11% of sequenced cases in the UK. As of October 20, the variant was reported in 33 countries, including Canada.
  • A subsequent technical briefing released on October 29, suggests that there is no evidence vaccine effectiveness is reduced against this variant compared to Delta.



  • The WHO reported a 3% increase in weekly cases; the European region reported a 6% increase in weekly cases. Deaths in the European region increased by 12%. The highest number of new cases continue to be reported in the US and UK. The report notes that Delta now outcompetes all other variants, accounting for 99.5% of sequenced samples in the last 60 days (Weekly epidemiological update - 2 November 2021).