Since the start of COVID-19 vaccination, 12.5% of world population has received one dose of the vaccine at least. Globally, a total of 2.4 billion doses of covid-19 vaccines have been administrated and more than 33 million are being administrated every day.
According to Kirsten Lyke, from University of Maryland School of Medicine in Baltimore, we can`’t answer these questions for sure yet. But researchers will figure that out soon. Much of what we know about immunity from COVID-19 comes from the data of people who got infected by covid and recovered. For most people the immune memory follows the rules, says Ali Ellebedy, an immunologist at Washington University School of Medicine in St. Louis. If a person who is already recovered gets exposed to the virus again, the immune memory of the pathogen is crucial for the body to fight against the virus.
A recent study published in Nature suggests antibodies in the patients who had mild infections, decline rapidly in first 4 months after recovering (suggesting very short-lived immune memory). After 4 months it declines gradually in 7 months (suggesting it remains detectable till 11 months after infection).
With the people getting vaccinated, evidences are building that “vaccines provide similar protection atleast”. Suggesting boosters are not required in that duration. Still, we don`t know the future of vaccines after that mark.
Even if a vaccine provides long lasting immunity, viruses emerge into viral variants which can make the COVID-19 vaccines less effective against them as compared to the parent strains. Low vaccination rates in poor countries posses a risk of prolonged pandemic. Which can cause more variants and more variants means less effective vaccine, making booster shots more likely.
Some companies, including Pfizer, a leading vaccine producing company, are now testing booster shots to fight evolving variants. Early results from Moderna hint that people who received a booster shot that uses the version of a viral protein from the beta variant had antibodies that were better at stopping the variant from infecting cells compared with people who got a third dose of the original vaccine.
Boosters are not uncommon:
Among some other vaccines, boosters are used for Tdap vaccines (tetanus, diphtheria, pertussis). For example, a booster for the vaccine that protects against tetanus, diphtheria, pertussis, or Tdap, is recommended every 10 years. People who travel in countries with high levels of hepatitis A are advised to get a booster shot 12 months after their first doses.
J.S. Turner et al. SARS-CoV-2 infection induces long-lived bone marrow plasma cells in humans. Nature. Published online May 24, 2021. doi: 10.1038/s41586-021- 03647-4.
Mathieu, E., Ritchie, H., Ortiz-Ospina, E. et al. A global database of COVID-19 vaccinations. Nat Hum Behav (2021)