Despite this, there has been a recent surge in cases, with 37% of new active cases and 20% of hospital cases . The country has had to .
How can this be happening? There are several possible explanations:
- The herd immunity threshold has not been reached — 62% vaccination is likely not adequate with the vaccines being used
- Herd immunity is unreachable due to inadequate efficacy of the two vaccines being used
- Variants that escape vaccine protection are dominant in Seychelles
- The B.1617 Indian variant is spreading, which appears to be more infectious than other variants
- Mass failure of the cold-chain logistics needed for transport and storage, which rendered the vaccines ineffective
What does the country’s experience teach us about variants, vaccine efficacy, and herd immunity?
Let’s break this down.
Variants Can Escape Vaccine Protection
However, no comprehensive surveillance exists in the country to know what proportion of cases are due to the South African variant.
The UK variant B117, which is more contagious than the original strain, became the dominant variant in the United States. But the US still cases through vaccination, with most people receiving the Pfizer and Moderna vaccines.
Israel, where the UK variant was dominant, also has a very high vaccination rate, having vaccinated nearly 60% of its population with Pfizer. It found against any infection including asymptomatic infection, and Israel has seen a .
The United Kingdom has used a combination of Pfizer and AstraZeneca vaccines. More than 50% of the population have had a single dose and almost 30% are fully vaccinated. The country has also seen a significant decline in case numbers.
Seychelles needs to conduct urgent genome sequencing and surveillance to see what contribution variants of concern are making, and whether the Indian variant is present.
If the South African variant is dominant, the country needs to use a vaccine that works well against it. Many companies are making boosters targeted to this variant, but for now, Pfizer would be an option. In Qatar, local researchers found Pfizer had .
We Need to Use High-Efficacy Vaccines to Achieve Herd Immunity
However, using lower efficacy vaccines means more people need to be vaccinated. If the vaccine is 60% effective, the proportion needing to be vaccinated rises to 100%.
When you get an efficacy of less than 60%, herd immunity is not achievable.
How much of the population needs to be vaccinated for herd immunity?
However, these calculations were done for the regular COVID-19 caused by the D614G variant, . This has a reproductive number (R0) of 2.5, meaning people infected with the virus on average infect 2.5 others.
What’s more, the Indian variant B1617 has been estimated to be at least 50% more contagious than B117, which could take the R0 to over 7, and takes us into uncharted territory.
This could explain the catastrophic situation in India, but also raises the stakes for vaccination, as lower efficacy vaccines will not be able to contain such highly-transmissible variants effectively.
A using very low efficacy vaccines would result in the economy barely breaking even over ten years because it would fail to control transmission. On the other hand, using very high efficacy vaccines would result in much better economic outcomes. More contagious variants mean more people need to be vaccinated to achieve herd immunity.
Vaccinating the World Is the Only Way to End The Pandemic
As the pandemic continues to worsen in some parts of the world, the risk increases of more dangerous mutations that are vaccine-resistant or too contagious to control with current vaccines.
Keeping up with mutations is like whack-a-mole while the pandemic is raging.
The take-home message for our pandemic exit strategy is that the sooner we get the whole world vaccinated, the sooner we will control emergence of new variants.
(C Raina MacIntyre is a Professor of Global Biosecurity, NHMRC Principal Research Fellow, and Head of the Biosecurity programme, Kirby Institute, UNSW. This is an opinion piece and the views expressed above are the author’s own. The Quint neither endorses nor is responsible for the same. This article was originally published on The Conversation. Read the original article here.)