World Immunization Week 24-30 April 2023


World Immunization Week 2023 aims to highlight the protection offered by vaccinations against transmissible diseases and to help resume the vaccination programs that were postponed during the pandemic

Looking back in the emergence of COVID-19 in the early rise of 2020, the global community, and especially so biomedical engineers and health scientists, wishing we already had a vaccine, raced against time to develop one. A unique, challenging race, and a first ever wide collaboration took place between biotechnological, pharmaceutical, medical and artificial intelligence experts with health and state authorities worldwide. The results justified the efforts. In less than a year, research has led to the development and manufacture of several vaccines that are currently available and administered according to the vaccination schedule of each country. COVID-19 Vaccines Global Access (COVAX), led by the World Health Organization (WHO) in collaboration with the Global Vaccine Alliance (Gavi), the Coalition for Epidemic Preparedness Innovations (CEPI) and UNICEF, aims to ensure equal access for all countries worldwide1.“A global pandemic requires a world effort to end it – none of us will be safe until everyone is safe”2.

As of April 22, 20213 929,000,000 doses have been given globally, 213 million individuals are fully vaccinated representing 2,7% of the world population. In Greece, 2.6 million doses have been given, 774.000 individuals are fully vaccinated representing 7.2% of the Greek population.

Currently available vaccines against COVID-19 have been developed based on three different technologies; using a different vehicle, vaccines present the human organism the information to create the characteristic spike protein and train the immune system to fight SARS-CoV-2:

  • Viral vector-based vaccines use a non-pathogenic (innocent) adenovirus to bring the information for the spike protein production: Astra Zeneca, Johnson & Johnson Janssen, Sputnik V
  • mRNA based use the part of SARS-CoV-2 mRNA that contains the code for spike protein synthesis: Moderna, Pfizer-BioNTech
  • Protein-based use directly the spike protein: Novavax (pending authorisation)

Most vaccinations lead to none or mild, self -limited symptoms (sore arm, fever, chills, myalgias), or less frequently allergic reactions.

However, a very rare type of adverse reaction has been recently observed, following millions of viral vector vaccine doses administered. The reaction involves a thrombosis with thrombocytopenia syndrome (TTS), in unusual sites, such as the cerebral venous sinus (CVST) and splanchnic vein thrombosis4.4The syndrome is considered to be caused by the activation of an autoimmune mechanism, similar to the HIT (Heparin Induced Thrombocytopenia- observed in some individuals treated with heparin), thus termed VIIT (Vaccine Induced Immune Thrombosis with Thrombocytopenia).5.

Symptoms that might be linked to VIIT include breathlessness, chest pain, leg swelling, abdominal pain, persistent headache, blurred vision and petechiae (blood spots under the skin)6.

As per the 4th April 2021 data, in a total of 34 million individuals having been vaccinated, 169 cases of CVST and 53 cases of splanchnic vein thrombosis including 18 fatalities, had been reported to EU drug safety database (EudraVigilance). All cases were extensively reviewed by (PRAC) the EMA safety Committee, who stated that the syndrome is very rare and the benefits of vaccination outweigh the risk7.

To put things in perspective, the risk for VIIT is 1 case in 250.000 vaccinated people, while the risk for thrombosis by the contraceptive pill is 1 in 2000 and that of long air travel 1 in 1000/year8.

Furthermore, COVID-19 patients are at increased risk of developing thromboembolic disease. Specifically, the risk is estimated as 11.2% for deep vein thrombosis,7.8% for pulmonary embolism, and 30% for thrombocytopenia, while 23% of those admitted in the intensive care unit will develop venous thromboembolism9.

Taking into consideration all facts and numbers it becomes evident that indeed the benefits outweigh the risks. Vaccination is the only effective way to prevent COVID-19, preserve our health and resume normalcy. It happened so many times before for diseases unbeknown to the younger among us.

It happened so many times before for diseases unbeknown to the younger among us. 200 years of vaccination history and experience prove the benefits:

  • Eradicate transmissible diseases and prevent future outbreaks
  • Improve morbidity and mortality at an individual and population level
  • Prevent disease, reduce disease severity and prolong life expectancy
  • Create herd immunity protecting those who cannot be vaccinated (i.e infants)
  • In preventing infectious diseases, vaccines also protect from certain types of cancer related to the initial infection (i.e HPV virus/cervical cancers among women)
  • Prevent antibiotic resistance
  • Reduce the financial burden on health care systems
  • Vaccines are safer than disease and respective medical treatment

It is noteworthy that the current pandemic as difficult and challenging as it is, has given us some positive opportunities:

  • The fast exchange and dissemination of medical knowledge as the disease was unfolding
  • The fast development of tests, therapeutic protocols and vaccines
  • The pharmacovigilance and safety protocols in real time function
  • The vast, big data size of information collected, analysed and interpreted in no time
  • The advanced technological abilities of our era and the fast forward boost to embrace new technologies in short time
  • The amazing results of selflessness and volunteerism especially among healthcare workers
  • The worldwide collaborative potential exhibited by countries, industries, scientific and technologic communities and philanthropists

In this global effort everybody has a role to protect their own health and the health of their fellow citizens, family and friends. When facing a transmittable disease, our best option and the most effective one is to get vaccinated.

“Prevention is better than cure”

as Hippocrates said


5. Schultz NH, IH Sørvoll, AE Michelsen, LA Munthe, F Lund-Johansen, MT Ahlen, M Wiedmann, et al. 2021. “Thrombosis and Thrombocytopenia after ChAdOx1 nCoV-19 Vaccination”. The New England Journal of Medicine.
8. Mahase, Elisabeth. 2021. 2021. “AstraZeneca vaccine: Blood clots are “extremely rare” and benefits outweigh risks, regulators conclude”. BMJ. 373. 373.
9. Tan BK, S Mainbourg, A Friggeri, L Bertoletti, M Douplat, Y Dargaud, C Grange, H Lobbes, S Provencher, and JC Lega. 2021. 2021. “Arterial and venous thromboembolism in COVID-19: a study-level meta-analysis”. Thorax.