What are the challenges of COVID-19 vaccination and herd immunity?

A recent study published in of clinical respiratory journal Vaccination against coronavirus disease 2019 (COVID-19) and herd immunity.

More than 6.5 million people have died worldwide due to COVID-19. Multiple outbreaks of his COVID-19 have been witnessed, mainly due to variants of the causative virus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Limiting continued transmission of SARS-CoV-2 variants has been difficult. The current study outlines SARS-CoV-2 subspecies and challenges in vaccination and herd immunity.

SARS-CoV-2 variants

SARS-CoV-2 continuously adapts to its host and acquires mutations over time, resulting in mutants that (potentially) exhibit properties superior to the ancestral strain. Most mutations have no or little effect on viral traits, but some affect virulence, transmissibility, and disease severity.

mutation of spike proteinFor example, alpha and delta mutants increase the affinity between the receptor-binding domain (RBD) of the spike and host cell angiotensin-converting enzyme 2 (ACE2). The World Health Organization (WHO) has designated emergency variants as variants of concern (VOC) or variants of interest (VOI) based on prevalence and characteristics.

Five VOCs have been identified so far: Alpha, Beta, Gamma, Delta and Omicron. The SARS-CoV-2 alpha genome has 17 mutations, including 8 in the spike protein. The beta mutant strain had a 50% higher infection rate than the wild-type strain and was associated with an increased risk of hospitalization, severe illness, and death. The gamma variant was twice as contagious as the ancestral strain.

SARS-CoV-2 Delta is causing more infections than previous infections and causing severe symptoms in unvaccinated populations. Notably, the risk of hospitalization for the Delta variant was double that for SARS-CoV-2 Alpha. The Omicron variant has the most mutations. In addition, several subvariants of SARS-CoV-2 Omicron have been identified. Studies have reported that previous SARS-CoV-2 infections were weakly protective against Omicron BA.4/5.

antiviral drugs, vaccination, herd immunity

Various antiviral drugs are being tested in clinical studies. Paxlovid is an antiviral drug that inhibits the activity of 3-chymotrypsin-like (3CL) protease, also known as the major protease of SARS-CoV-2. Preliminary findings show that when administered within 3 days of the onset of symptoms, paxlovid was superior to mornupiravir in reducing the risk of hospitalization in patients by 89% compared to placebo subjects and in reducing the risk of hospitalization by 50%. It suggests that

SARS-CoV-2 vaccines are highly effective in reducing the risk of symptomatic or asymptomatic disease. In addition to increased transmissibility/virulence, SARS-CoV-2 variants have acquired immune evasion properties, weakening the protection conferred by vaccination. Nonetheless, some vaccines are somewhat effective against SARS-CoV-2 variants.

For example, the ChAdOx1 vaccine was effective against SARS-CoV-2 alpha. Pfizer’s BNT162b2 vaccine was 91% effective against Qatar beta. Both ChAdOx1 and BNT162b2 vaccines are effective against SARS-CoV-2 Delta, with the latter more effective than the former.

Herd immunity is essential for epidemic control. A significant proportion of the population must be immune to prevent large outbreaks. Studies suggest that immunity from previous infection with pre-omicron variants is 15% to 28% protective against re-infection with SARS-CoV-2 omicron BA.4 or BA.5 subvariants It has been.

In contrast, Omicron BA.1 or BA.2 infection-induced immunity provided 76% to 79% protection against reinfection with BA.4 or BA.5. Some data-driven models are 74% of vaccines Effectiveness, vaccination coverage must exceed 93% to achieve herd immunity. Current vaccination coverage is low and needs to increase to achieve herd immunity.

COVID-19 incidence in children

Notably, the incidence of COVID-19 is lower in children than in adults, and mortality is much lower in the early stages of the pandemic. However, data from Malaysia suggest that COVID-19-related child mortality was higher during the delta wave. In addition, another study reported that children and adolescents are about five times more likely to be hospitalized than adults. As a result, multiple countries have approved the vaccination of children from her 5 years old to her 11 years old.

Vaccination Priorities and Vaccine Skepticism

COVID-19 vaccination programs prioritize the most vulnerable groups, such as health care workers (HCWs), those receiving essential services, those with compromised immune systems, and comorbidities, over others. We are implementing a prioritization strategy so that

Some people refuse to be vaccinated, believing that the risk of infection is low, while others are skeptical because of safety concerns or a lack of trust. Interactions with people influence vaccination decisions. Social pressure and encouragement from trusted and influential peers increases vaccine uptake.

in conclusion

Overall, more efforts are needed to improve vaccination coverage, especially among priority groups who have not yet been vaccinated. Additionally, non-pharmaceutical interventions such as physical distancing, face masks, and proper ventilation in indoor environments should be properly implemented to contain the COVID-19 pandemic.