Journey to Herd Immunity

When will life return to normal? It’s the question on everyone’s mind, as the first sizable tranche of vaccines touched down on T&T’s shores this past week. Becoming vaccinated may not be the silver bullet needed to eradicate COVID-19, but each shot administered would be one step closer to herd immunity—a possible end to the pandemic.

As defined by the World Health Organization (WHO), herd immunity is “the indirect protection from an infectious disease that happens when a population is immune either through vaccination or immunity developed through previous infection.”

The best way to achieve herd immunity is through vaccination, not widespread infection, resulting in unnecessary cases, deaths, and more variants like we’ve seen in the UK, Brazil, and South Africa.

A substantial portion of the population would need to be vaccinated to achieve herd immunity, but how much is “substantial?” Depending on how contagious an infection is, usually, 50 per cent to 90 per cent of a population needs immunity to achieve herd immunity. For measles, 95 per cent of the population needs to be vaccinated, meaning the remaining five per cent would be protected as measles will not spread among the vaccinated. For polio, that threshold was 80 per cent.

For COVID-19, there is still not an established metric, with the WHO stating, “the proportion of the population that must be vaccinated against COVID-19 to begin inducing herd immunity is not known.”

In T&T, the Ministry of Health has chosen 75 per cent to be our herd immunity threshold. Based on the WHO’s current guidelines, vaccines are only suitable for those over the age of 18. Thus, T&T would need 1,476,143 doses to vaccinate 738,071 people.

The Minister of Health, Terrance Deyalsingh, said the Ministry aims to administer at least 1,000 doses per day. At this pace, if the entire vaccine-eligible population was inoculated, it would take over four years.

However, at Thursday’s Ministry of Health news conference, he clarified, “We have plans for phase two and phase three for more sites, mass vaccination sites at that time. After we get enough of a body of knowledge of how we are responding to the vaccine, we are not seeing major side effects; we’ll ramp up more and more and more.”

For Phase One of T&T’s vaccine rollout programme, the Ministry aims to inoculate high-risk, frontline healthcare workers and people aged 60 and over with non-communicable diseases (NCDs). Specifically, the Ministry selected 6,621 from a pool of 16,000 to 17,000 public healthcare workers. For the public with NCDs, the Ministry aims to vaccinate 40,950 people in the first instance who met the age criteria. Minister Deyalsingh added, “Obviously, the 33,000 would not cover all, but it would make a serious dent,” with the outstanding COVAX vaccines covering the remainder.

Chief Medical Officer Dr Roshan Parasram, before a Joint Select Committee on Wednesday, explained the number of people within Phase One might be substantially higher, “in the region of 400,000.” If the Ministry maintains the 1,000 doses per day pace, it will take over two years to complete this phase. The health minister reiterated the vaccination rollout would be scaled as needed.

Officials remain silent on when T&T would achieve specific vaccination threshold targets purely because the government still does not have firm dates for vaccine delivery or finalised quantities. One factor that hasn’t been taken into account would be the role of the private sector. As private entities gain access to vaccines over the coming months, their employees would be vaccinated, and companies may aid in the national vaccine rollout programme, speeding up our journey to herd immunity.