Page 11 - IJPS-11-5

International Journal of
Population Studies Human behaviors during the COVID-19 pandemic

Figure 3. Percentage of viral load in symptomatic and asymptomatic individuals. Image obtained from Yang et al., 2021.

6.1. Pharmaceutical interventions low vaccination rates in the US, achieving herd immunity
Even though SARS-CoV-2 is highly infectious, the through vaccination alone became unattainable.
infection can be prevented primarily through vaccinations Furthermore, as the variants evolved, SARS-CoV-2
and/or therapeutics. When the initial messenger RNA evaded vaccine protection. By the end of 2023, protection
vaccine trial results were published in December 2020, against infection from the XBB.1.5 Pfizer booster was 35%
the prospect of achieving herd immunity and ending the (95% CI: 10–52%) among 18–59 year olds and 55% (95%
pandemic seemed within reach. Moderna’s vaccine showed CI: 48–61%) among 60–85 year olds (Huiberts et al., 2024).
94.1% efficiency (95% CI: 89.3–96.8%) (Baden et al., 2020) Furthermore, for unknown reasons, COVID-19 vaccine
and Pfizer’s demonstrated 94.8% efficacy (95% CI: 89.8– protection quickly waned with time. While some vaccines,
97.6%) (Polack et al., 2020) against the infection. These for example, measles and polio, confer lifetime immunity,
spectacular results took many by surprise. COVID vaccines require annual updates and boosters every
The proportion of the population that must be immune 6 months. Other than vaccinations, there are two other
from infection to achieve herd immunity is greatly therapeutic approaches to avoid infection: monoclonal
influenced by R , which reflects how many people an antibodies and 5% iodine nasal spray and/or gargle.
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average person will infect in a new environment. With 6.1.1. Monoclonal antibodies
~95% vaccine effectiveness against infection and the
Wuhan strains’ R of 2.5, roughly 65% of the population The two that were approved for use to prevent COVID-19
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needed to be vaccinated or previously infected to achieve infection in the US were Evusheld (tixagevimab and
herd immunity. However, with Delta’s higher R of 5 and the cilgavimab) and Pemgarda.
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Volume 11 Issue 5 (2025) 5 https://doi.org/10.36922/IJPS025110040