Vaccinating the whole world against smallpox was one of the most important scientific achievements of the 20th century. Smallpox is a great example of the success of vaccine-mediated eradication of a deadly virus in humans which required a global initiative that combined high levels of vaccine coverage and active surveillance.1

How viruses spread

Transmissibility and virulence (severity) are the two factors which play a major role in the spread of a virus from isolated infections or epidemics limited geographically to global pandemics. Ebola virus outbreaks continue to occur in West Africa.2 There is a very low likelihood that Ebola would ever cause a major pandemic since the virus is highly pathogenic leading to very high mortality. This results in the infected perishing before the virus can be widely dispersed throughout the general population. Ebola and H5N1 virus are highly virulent but poorly transmissible, both leading to high mortality numbers but lower overall infections.3 

On the other side of the spectrum, coronaviruses that cause common cold illnesses have extremely efficient transmission capabilities and lead to pandemics every year.4 However, since these viruses have low virulence, leading only to upper respiratory tract symptoms in most patients, they have never been newsworthy. 

SARS CoV-2 causing COVID-19 disease is more of a spectrum of diseases rather than a simple virus. The mutations, which were identified from Alpha, Delta to Omicron, make each subsequent strain much more efficient in transmission, yet fortunately lower in virulence.5 However, the evolution of COVID-19 to the low level of virulence seen in common cold coronaviruses may not occur, or may take several decades to manifest.6 

“Advanced communication and technology led to a worldwide effort developing vaccines at a record pace. Today, we are close to the end of the pandemic.” 

– Dr. Younes

Establishing population immunity

What is more of a certainty is that the severity of the disease caused by SARS-CoV-2 has decreased with increasing population immunity. In patients with pre-existing immunity due to vaccination, a subsequent infection with SARS-CoV-2 leads to decreased severity of symptoms after infection.7 

On a local level in the Coachella Valley, at the largest medical center, 90 percent of individuals who developed severe symptoms related to COVID-19 since June 2021 are unvaccinated. 95 percent of ICU admissions are unvaccinated. 98 percent of patients who died from COVID-19 related illnesses were not vaccinated. The only vaccinated patients who developed severe illness were unfortunately suffering from immune altering co-morbidities.* 

On a global level, strains like the Delta variant are easy to transmit with one patient spreading the disease to three people. The Delta strain is considered extremely pathogenic causing a mortality rate of about two percent (i.e., two patients die out of every 100 infected patients). A few mutations later, Omicron strain has adapted much more readily to its environment. This makes it highly likely to transmit between individuals so that every patient spreads the disease to 12 people, also known as the reproductive number (Ro). Contextually, the measles virus, an old scourge previously declared eliminated from the U.S., has re-emerged in the past few years as the cause of multiple outbreaks across the country due to lower levels of vaccine coverage as a direct effect of anti-vaccination movements.8 Measles has a very high reproductive number and can be transmitted to 15 susceptible individuals from one infectious case.9 

The mortality rate for Omicron is 0.25 percent (i.e., one patient dies out of every 400 infected patients). This strain, and the next mutation that will occur, will lead to herd immunity and the transformation of the pandemic to an epidemic.1  In most cases, herd immunity is not achievable without an effective vaccine,11 as vaccines enhance and hasten the development of a higher immunity level in the population reaching a herd immunity level.

Learning from the past

The Spanish flu, a misnomer since it started in Kansas12 and killed millions of people, had an extremely high mortality rate at the beginning of the pandemic. Theoretically, mutations developed as more people became infected and subsequently less people died from the disease. Eventually, effective vaccination was developed against the virus. Each year, scientists identify the most likely strains to cause seasonal outbreaks and hence new formulations of Influenza vaccination are administered saving millions of lives worldwide. A century after the flu pandemic, another virus is holding the world hostage as COVID-19 has killed millions of people globally. 

In summary, advanced communication and technology led to a worldwide effort developing vaccines at a record pace. Today, we are close to the end of the pandemic. Viruses are host-dependent for survival and are not self-sustaining. In other words, if the host dies, the virus dies. In an epidemic or pandemic setting, evolution leads viruses to develop mutations that make them easier to transmit and propagate between hosts, at the expense of becoming less pathogenic, like in the case of coronaviruses previously introduced into the population. 

As an infectious diseases specialist and a public health expert, I rely on scientific evidence where data is derived from studies which are based on experimentation and reproducible statistics. Unfortunately, there are many myths about the virus online, as the enemy of science is fame. Unsubstantiated rhetoric about vaccines that is not backed by evidence is misleading, and as we have unfortunately seen, is potentially harmful to the general population. 

Dr Younes is an infectious diseases specialist, founder of Desert Infection Consultants (DIC) and a member of Desert Doctors. He would like to thank DIC Kinji Hawthorne, MD, MPH and Roula Younes, DNP for their assistance in research, editing and co-authoring this editorial. For more information, visit www.younesmedicalcenter.com. (760) 636.1336.

References: 1) Sci Am1976 Oct; 235(4):25-33. doi: 10.1038/scientificamerican1076-25; 2) https://www.everydayhealth.com/ebola/guide/outbreaks; 3) Osterholm, M. T. & Kelley, N. S. Mammalian-transmissible H5N1 influenza: facts and perspective. MBio 3, 2 (2012); 4) www.cdc.gov/coronavirus/general-information.html; 5) Nature, vol 596. 26 August2021 p497; 6) www.nature.com/articles/s41576-018-0055-5; 7) https://pubmed.ncbi.nlm.nih.gov/33658326; 8) Paules CI, Marston HD, Fauci AS. Measles in 2019 – Going Backward. New England Journal of Medicine. 380 (23), 2185-2187 (2019); 9) Sanche, S. et al. High contagiousness and rapid spread of severe acute respiratory syndrome coronavirus 2. Emerg Infect. Dis. 26, 1470-1477 (2020); 10) www.worldometers.info/coronavirus; 11) https://www.lung.org/blog/understanding-covid-herd-immunity; 12) www.army.mil/article/188078/scientists_learn_history_of_spanish_flu_at_fort_riley

*Data collected by author individually from Eisenhower Medical Center electronic medical records. No patient identifiers included. Data collected was used purely for statistical analysis.

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