An interesting article published by Pawlowski and others in Scientific Reports published 26th February 2021 investigated this issue.  

Conventionally, vaccinations are intended to train the adaptive immune system by generating an antigen specific immune response. 

However, studies are also suggesting that certain vaccines lead to protection against other infections through trained immunity for up to one year and in the case of live vaccines for up to five years. 

For instance, vaccination against smallpox showed protection against measles and whooping cough.  Live vaccinia virus was successfully used against smallpox. 

In this study, they conducted a systematic analysis to determine whether or not a set of existing non COVID-19 vaccines in the United States were associated with a decreased rate of SARS-CoV-2 infection.  

They considered data from 137,037 individuals from the Mayo Clinic electronic health record database who had received PCR tests to SARS-CoV-2 between February 15th 2020 and July 14th 2020. 

They found that if immunisation for polio, haemophilus influenza type B, measles, mumps, rubella MMR, varicella, pneumococcal conjugate, geriatric influenza and hepatitis A/hepatitis B had been administered, these vaccination patients were associated with a lower rate of SARS-CoV-2 infection.  

Vaccination with another 11 vaccines, typhoid, tetanus, herpes zoster, rotavirus, PCV23 pneumococcal pneumonia, paediatric influenza, meningococcal, live influenza, general influenza, HPV were not associated with a lower incidence of SARS-CoV-2 infection. 

This was even after adjusting for geographic SARS-CoV-2 incidence and testing rates, demographics, comorbidities and number of other vaccinations.  This was also if the vaccines had been administered in the past one, two and five years. 

Furthermore, age, race/ethnicity, and blood group stratified analyses revealed significantly lower SARS-CoV-2 rate among black ethnic origin individuals who had taken the pneumococcal PCV13 vaccine. 

Ongoing clinical studies offer preliminary evidence that existing vaccines may reduce the risk of SARS-CoV-2 infection for example.  The interim results from the ACTIVATE trial indicate that the BCG vaccine reduces SARS-CoV-2 infection rates by up to 53%.

Overall, the study identified existing approved vaccines which could be promising candidates for preclinical research and randomised clinical trials towards combating COVID-19.

Dr Paul Ettlinger

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