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Without booster shots, loss of protection against COVID-19 infection in the coming months could lead to new epidemic waves

Young woman receiving a vaccination at a clinic

The Pfizer vaccine protects against infection with COVID-19 according to a recent study published in the NEJM from Qatar and co-authored by Aspen Medical Group Medical Director, Dr Andrew Jeremijenko.

It is even more effective at protecting against severe disease and hospitalisation with over 90'% protection. The protective level of the vaccine builds rapidly even after the first dose, then peaks in the first month after the second dose. The protection against severe and critical and fatal disease persists at high levels (> 90%) for at least six months. The level of protection falls against mild and asymptomatic infection between 2 and 6 months and in this study, protection fell to less than 20% against mild infections at 6 months, despite the high level of protection against severe, critical and fatal disease. Vaccine breakthrough infections were found to be less infectious than primary infections in unvaccinated persons, suggesting lower levels of spread would occur.

The immunisation campaign in Qatar prioritized vaccination of persons with severe or multiple chronic conditions and prioritised vaccination according to age group, this pattern of waning of protection could theoretically be confounded by effects of age and coexisting conditions. Vaccinated persons presumably have a higher rate of social contact than unvaccinated persons and may also have lower adherence to safety measures and this behaviour could reduce real-world effectiveness of the vaccine as compared with its biologic effectiveness, possibly explaining the waning of protection.

These findings suggest that a large proportion of the vaccinated population could lose its protection against infection in the coming months, perhaps increasing the potential for new epidemic waves.

The US Centers for Disease Control and Prevention recommended that people older than 65, people with conditions making them more susceptible to getting seriously ill with breakthrough infections, and people at high risk of infection such as healthcare workers and prison inmates get boosters. Australians aged 12 and older who are considered severely immunocompromised are eligible for a booster shot. Formal advice from the Australian Technical Advisory Group on Immunisation (ATAGI) is expected by the end of October on how booster shots might be rolled out to the general population, including health workers and older Australians.

Dr Andrew Jeremijenko is a specialist in Occupational and Environmental Medicine as well as a qualified General Practitioner and epidemiologist. He has worked in Australia, Asia and the Middle East.