Do Vaccines Really Work?

The short answer is yes. Most of us have nearly forgotten about deadly diseases like measles or smallpox thanks to vaccines. Measles vaccines have saved an estimated number of at least 21 million lives since 2000¹, and smallpox vaccines have eliminated smallpox in the world since 1980². So why do we catch flu and need a new flu shot every year? The reason lies in the ever-changing nature of the genomes of viruses because of “mutations.” Once a viral genome changes to a point where it is no longer recognized by the immune system trained by the vaccine received in the past, the old vaccine becomes ineffective or useless.

Can a single administration of the COVID-19 vaccine or one-time COVID-19 infection protect us for life? It depends on how fast the virus mutates and how our immune system holds up. SARS-CoV-2 is an RNA virus, and its RNA genome naturally keeps changing. Research showed that the virus has already mutated since the beginning of the global outbreak³. This means that two COVID-19 patients might be infected by different strains of SARS-CoV-2. Viral mutations are not necessarily bad—mutations often do not affect the virus or even make it a weaker pathogen⁴. However, a changing viral genome means that the protection offered by the vaccine made with another “version” of the virus might not last. Moreover, the defense built by our immune system might weaken over time and need to be reinforced. In fact, a recent study showed that the neutralizing antibodies produced in a large proportion of recovering patients lasted only for 2–3 months, suggesting that long-term immunity against COVID-19 might require repeated vaccine administration⁵. This also means that a COVID-19 infection might not guarantee life-long safety. As knowledge about SARS-CoV-2 unfolds, we will learn whether single or repeated vaccine administration can adequately keep us healthy for life.

Elimination vs Eradication: What Is the Difference?

Imagine that we now have an effective treatment for COVID-19. Do we still need a vaccine? The answer is yes. Treatment can help eliminate the disease but not eradicate it⁶. Even if every single patient in New York City has been treated for COVID-19 and recovered, it takes just one traveler carrying the virus to re-introduce another COVID-19 outbreak. When COVID-19 no longer circulates in New York City, it is considered eliminated in this region. When COVID-19 is eliminated worldwide and has no chance to be re-introduced, it is considered eradicated. Eradication is key to returning to a time that we fully enjoy traveling and being in the presence of each other, as well as minimizing burdens on the healthcare system. Together, effective treatments and vaccines prevent diseases from spreading and repeating the history of pandemics.

 Sources and Further Reading

1. “Global Measles Outbreaks.” Centers for Disease Control and Prevention, 6 Mar. 2020, www.cdc.gov/globalhealth/measles/globalmeaslesoutbreaks.htm.
2. “Smallpox .” Centers for Disease Control and Prevention, 12 July 2017, cdc.gov/smallpox.
3. Phan, Tung. “Genetic Diversity and Evolution of SARS-CoV-2.” Infection, Genetics and Evolution, vol. 81, 2020, p. 104260. Crossref, doi:10.1016/j.meegid.2020.104260.
4. Garcia de Jesus, Erin. “Is the Coronavirus Mutating? Yes. But Here’s Why You Don’t Need to Panic.” Science News, 26 May 2020, www.sciencenews.org/article/coronavirus-covid19-mutations-strains-variants.
5. Long, Quan-Xin, et al. “Clinical and Immunological Assessment of Asymptomatic SARS-CoV-2 Infections.” Nature Medicine, 2020. Crossref, doi:10.1038/s41591-020-0965-6.
6. Dowdle, Walter R. “The Principles of Disease Elimination and Eradication.” Centers for Disease Control & Prevention, 2 May 2001, www.cdc.gov/mmwr/preview/mmwrhtml/su48a7.htm.