**2. Vaccines impact on the course of pandemic**

Despite all the issues and difficulties, the humankind succeeds enough against the SARS-CoV-2/COVID-19, returning to a new "normal" life, after a successfully deployed and globally aggressive plan of vaccination against SARS-CoV-2/COVID-19 with multiple vaccine types. Up to October 25, 2022, a total of 12,822,482,039 vaccine doses have been administered in the world, representing the largest historical effort in vaccination [44, 47–49]. Over these months, multiple studies on vaccine impacts, preclinical, phase 1, phase 2, phase 3 (efficacy), and phase 4 (effectiveness, real-world impact), as well as their corresponding side effects assessment, have been developed showing the high efficacy, effectiveness, and safety of the used anti-COVID-19 vaccines (**Figure 3**) [41, 50–53].

Using vaccines with 50% of efficacy, or more, some of them above 75–80%, together with other measures, transmission was affected, but particularly mortality. Additionally to the published studies (**Figure 3**), multiple countries (e.g., the United States of America) monitor data regarding incidence and mortality among nonvaccinated and vaccinated people.

Case fatality rate among those not-vaccinated according to some analyses in the United States of America reached up to 12 times higher than compared with

#### **Figure 3.**

*Phase 3 and phase 4 COVID-19 vaccine studies published in PubMed-indexed journals up to October 25, 2022.*

#### **Figure 4.**

*Rates of COVID-19 deaths by vaccination status and two or more (2+) booster doses\* in ages 50+ years. (https:// covid.cdc.gov/covid-data-tracker/#rates-by-vaccine-status).*

people with boosters, especially in elderly people (**Figure 4**). Anti-COVID-19 vaccines save lives.

For October 2022, multiple countries have applied a fourth dose or second booster in their populations. Obviously, the coverage at primary and booster schemes is highly variable among countries. Prioritizing vaccination coverage must remain as one of the key factors driving vaccine uptake [54]. Also, vaccine hesitancy is important and should be prevented with comprehensive population education [55].

It is now clear that none of the available COVID-19 vaccines provides robust, lasting protection against infection, particularly in the Omicron era, and likely due to inadequate and/or short-lived mucosal immunity [56, 57]. However, booster doses of all widely used vaccines offer very high levels of protection against severe outcomes [54]. With this consistency of protection against severe disease across different variants, the case for developing variant-specific vaccines becomes less urgent, particularly if heterologous schedules can potentially circumvent some of the challenges homologous schedules may encounter in the face of new variants [58–60].

### **3. Conclusions**

COVID-19 pandemic has not been over. Although the evolution during the last months, especially in 2022, has been significantly positive, still SARS-CoV-2 and its variants, particularly the sublineages of Omicron (**Figure 5**), continue changing and circulating. That means preparedness, vaccination, assessment, and research, considering this evolving scenario, should be considered and continuously applied.

*Introductory Chapter: Lessons from SARS-CoV-2/COVID-19 after Two Years of Pandemic DOI: http://dx.doi.org/10.5772/intechopen.108769*

#### **Figure 5.**

*Omicron sublineages over time, up to October 25, 2022. (https://www.gisaid.org/).*

Prevention is key in general, continued education, surveillance, and monitoring, has been essential, and still will be up to the time SARS-CoV-2 became endemic or disappear. Many lessons have been learnt at differential levels [61, 62], but is essential to be highly, and even, better prepared for the next pandemic, to be caused by a coronavirus, another zoonotic virus making a spillover [3, 62] (e.g., zoonotic Influenza or monkey pox) [63, 64], or in general by another emerging or remerging pathogen. In the future outbreaks, we cannot fall into some of the mistakes done during the COVID-19 pandemic [65]. We have to work on the impacts of COVID-19 on other infectious diseases, such as the decrease of vaccine coverages against other vaccine-preventable diseases [66], as well as to deal with long-COVID-19 syndrome [67], among others.

We need to be better prepared for viral threats, monitor risks, and increase our preparedness and effective responsiveness against outbreaks, epidemics, and pandemics, to promote a safer and healthier world.
