CME INDIA Presentation by Dr. Rajeev Jayadevan, MD, DNB, MRCP, ABIM (Med) ABIM (Gastro), NY. Vice Chairman, Kerala state IMA Research Cell. Member, National IMA Task Force on Corona Epidemic, Cochin.

An Impetus to Rethink

Vaccination Not Very Effective at Preventing Spread of Infection. So, What?

Needless to say that the primary aim of vaccination is to protect individuals against severe COVID-19 disease and its consequences. The key to contain epidemic is ability of vaccines to reduce onward transmission. One recent study has provided new impetus to rethink the strategies.

Lancet paper from UK October 28, 2021 tells a very unique story

  • Vaccinated people transmit virus as efficiently as unvaccinated people.
  • Vaccinated household contacts get infected almost as easily as unvaccinated contacts. They were only 13% less likely to become infected, compared to unvaccinated contacts – if delta enters household.
  • Protection against infection starts waning within 2-3 months after 2nd dose
  • Note: protection against severe disease and death does not decrease.
  • Viral load same in vaccinated (breakthrough) and unvaccinated infections.
  • This explains why there is so much transmission within individual homes even after ‘everyone in the family was vaccinated.’
  • This study is consistent with observations in India, including reports of large outbreaks among fully vaccinated communities from a few months ago.
  • This study was limited to symptomatic cases only; impact of asymptomatic transmission still unknown.
  • Study done in UK where Pfizer and AstraZeneca vaccines were used.

There is a need to redefine the objectives of vaccination

  • Although 2 doses of vaccine offer good protection against severe disease, vaccination is not an effective tool against preventing infection as was initially believed.
  • We must learn to accept these facts and move forward, than continue to hold on to outdated objectives.
  • The waning within 2-3 months raises concern about the purported role of “boosters” – what after 3 months?

CME INDIA Learning Points

  • It is well known that households are the site of most SARS-CoV-2 transmission globally.
  • Vaccination has been found to be effective in reducing household transmission of the alpha variant (B.1.1.7) by 40–50%.
  • Vaccination is effective in true sense as vaccinated individuals had lower viral load in the upper respiratory tract than infections in unvaccinated individuals. So, there is reduced infectiousness.
  • These days dominant strain worldwide is the delta variant (B.1.617.2), which is more transmissible than the alpha variant.
  • Delta variant did a large outbreak in India. Later UK was one of the first countries to report a sharp rise in delta variant infection.
Most important points of concern happening now:
Current vaccines remain highly effective at preventing admission to hospital and death from delta infection.
Vaccine effectiveness against infection is reduced for delta, compared with alpha.
The delta variant continues to cause a high burden of cases even in countries with high vaccination coverage.
Data are scarce on the risk of community transmission of delta from vaccinated individuals with mild infections.
  • ATACCC is an observational longitudinal cohort study of community contacts of SARS-CoV-2 cases. To ascertain secondary transmission with high sensitivity, researchers longitudinally followed index cases and their contacts (regardless of symptoms) in the community early after exposure to the delta variant of SARS-CoV-2.
  • They performed daily quantitative RT-PCR on URT samples for 14–20 days.
  • It was found that the secondary attack rate in fully vaccinated household contacts was high at 25%, but this value was lower than that of unvaccinated contacts (38%).
  • Point of Concern: Risk of infection was found to be increased with time in the 2–3 months since the second dose of vaccine.
  • The study observed transmission of the delta variant between fully vaccinated index cases and their fully vaccinated contacts in several households. It was confirmed by whole-genome sequencing.
  • Although the peak viral load did not differ by vaccination status or variant type but did increase modestly with age.
  • Vaccinated persons, when infected with delta strain, experienced faster viral load decline than did unvaccinated alpha or delta cases.
  • As these findings are derived from community household contacts in a real-life setting, they are probably generalisable to the general population, as per researchers.
  • Mystery solved? These findings help to explain how and why the delta variant is being transmitted so effectively in populations with high vaccine coverage.
  • The study suggest that vaccination alone is not sufficient to prevent all transmission of the delta variant in the household setting, where exposure is close and prolonged.
  • So, we need to think seriously to increase population immunity via booster programmes.
  • Most important message remains valid: Those who were vaccinated cleared the virus more quickly and had milder cases, while unvaccinated household members were more likely to suffer from severe disease and hospitalization.

CME INDIA Tail Piece

Vaccination Not Very Effective at Preventing Spread of Infection. So, What?


1. Anika Singanayagam, Seran Hakki, Jake Dunning, Kieran J Madon, M. et al.Community transmission and viral load kinetics of the SARS-CoV-2 delta (B.1.617.2) variant in vaccinated and unvaccinated individuals in the UK: a prospective, longitudinal, cohort stud.Lancet Infect Dis 2021 Published Online October 28, 2021 S1473-3099(21)00648-4 SeeOnline/Comment S1473-3099(21)00690-3

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