One year on from when many Kiwis got their first COVID-19 booster vaccine, how is the country’s immunity holding up?
The SMC asked experts to explain where we’re at with boosters and the latest on Omicron-specific “bivalent” booster jabs.
Professor Michael Plank, Te Pūnaha Matatini and University of Canterbury, comments:
“It is now around a year since many New Zealanders received their last Covid-19 vaccine. A large proportion of the population has since been infected by the virus, providing a natural boost to immunity albeit by an unwelcome route. However, there is probably still at least half the population whose last vaccine dose or infection was more than six months ago.
“Covid-19 is still causing or contributing to 30-40 deaths every week and will continue to inflict a significant health burden. Alongside antiviral treatments, vaccines are by far the best tool we have to minimise illness and death.
“New Zealand has at least two routes available to increase levels of immunity using vaccines. The first is to continue efforts to reach those who are currently eligible for a vaccine dose, especially groups where risk is high or uptake is low. These include Māori and Pacific peoples, and the elderly. More than half of over-50s are still due for either their first or second booster. Using vaccination to top up immunity levels among older adults aged 50-plus will go a long way to reducing the health burden of Covid-19.
“The second potential route is to start offering so-called bivalent vaccines as many countries are now doing. These updated vaccines contain mRNA-encoding proteins from both the original 2020 strain of the virus and an Omicron variant (either BA.1 or BA.4/5). Although the virus continues to evolve its ever-growing family tree, using Omicron-based vaccines will provide a better match to currently-circulating variants, which are all part of the Omicron family. They may also broaden our immune response, meaning our immune system is less likely to be blindsided by a future new variant.
“England has offered these bivalent vaccines to over-50s since September 2022 and around 65% have since had a dose. Data shows that these vaccines halve the risk of hospitalisation for Covid-19 compared to people whose last dose was more than six months ago. I hope New Zealand will start to use these updated vaccines in the near future.”
Conflict of interest statement: “I receive funding from the Department of Prime Minister and Cabinet and the Ministry of Health for mathematical modelling of Covid-19.”
Associate Professor Dianne Sika-Paotonu, Immunologist, Associate Dean (Pacific), Head of University of Otago Wellington Pacific Office, and Associate Professor, Dean’s Department, University of Otago Wellington, comments:
“Although we are in the middle of summer here in Aotearoa New Zealand, we’re continuing to experience impacts of the current Omicron wave, with future Covid-19 waves still likely.
“One of the latest Omicron subvariants is “Kraken”, otherwise known as XBB.1.5 (an offshoot of Omicron XBB), and carries an important mutation called “F486P”. The XBB.1.5 (Kraken) subvariant is responsible for a sharp rise in cases in the USA, and was reported in 38 countries by the WHO in early January 2023.
“Kraken has mutated in a way that enhances overall transmissibility and neutralising-antibody evasion ability of this subvariant. Stronger binding between the virus and the ACE-2 receptor occurs, with the virus also better able to evade the body’s neutralising-antibody protection. At the end of 2022, the WHO indicated there was also early evidence of higher reinfection risk associated with the XBB.1.5 (Kraken) subvariant. Whether or not it causes more severe illness has yet to be determined.
“The current Covid-19 boosters available in Aotearoa New Zealand consist of an extra dose(s) of the vaccine given after the primary course. The newer bivalent Covid-19 boosters, contain mRNA coding for the original virus strain (– giving broad protection against COVID-19), plus an mRNA code common between the Omicron variant BA.4 and BA.5 lineages (– giving better protection against Omicron specifically). Determining how effective the currently-available bivalent vaccines are against new Omicron sub-variant XBB.1.5 (“Kraken”) is still being worked through.
“On 21st December 2022 New Zealand’s Medsafe granted provisional approval for two Pfizer Covid-19 bivalent booster vaccines for Omicron BA.1, and Omicron BA.4/5 for those aged 12 years and over, who’d received at least two Covid-19 vaccine doses for their primary course. The Covid-19 Vaccine Technical Advisory Group has since been in the process of preparing advice for the government to decide whether or not to use these vaccines.
“New variants of the SARS-CoV-2 virus will continue to emerge, develop and spread, while issues with unequal global Covid-19 vaccine coverage, availability, accessibility and distribution persist, and remain unaddressed. Addressing health inequities and current inequities in society will be critical steps moving forward.
“Simple public health measures that include being up-to-date with vaccines and boosters, isolating when sick, testing, wearing a mask where possible, proper ventilation, being outdoors, and other public health measures, remain important steps to (1) help protect against the most severe impacts of Covid-19, (2) help protect against reinfection, and also (3) help protect against other illnesses still circulating at this time.”
No conflicts of interest declared.
Professor Nikki Turner, Director Immunisation Advisory Centre, University of Auckland, comments:
“Evidence continues to clearly show the effectiveness of a course of the mRNA Comirnaty COVID-19 vaccine against severe disease, but it is relatively less effective for mild disease or transmission. So many of those vaccinated will still catch COVID, but most will avoid severe disease.
“The virus has evolved from the original strains through to a range of Omicron strains. It is clear that for all adults, a primary course of two doses, plus a booster, is needed to reduce the risk of severe disease – i.e. being hospitalised or dying from COVID disease. The vaccine does have some effect against mild disease and reducing transmission – but to a lesser extent, and it is this protection that wanes fairly fast. There are still a lot of people who haven’t had their first booster and for healthy adults we should concentrate on getting that first booster, rather than offering extra boosters.
“For healthy adults, two vaccine doses plus having one booster (2 + 1) is important protection against Omicron strains. Having mixed immunity is good too, that is, for people who have had vaccinations and then also had COVID infection. Even if it’s many months from the first booster shot, for most people protection from severe disease continues.
“A second booster is used for people at higher risk, the elderly or those with other health problems, i.e. when their immune systems are compromised in some way. The extra booster helps them to lift their immunity so it’s closer to that of a healthy person with a first booster.
“Bivalent vaccines for COVID (that include a component of the original strain of COVID and an Omicron strain) have been tested internationally. The results to date do show a good immune response that has the potential to offer even broader protection than the current ‘monovalent’ vaccine. The New Zealand COVID-19 Technical Advisory Group will be considering these data in the coming weeks.
“So far the research done in the United States and Israel suggests that the use of a bivalent vaccine as a further booster can reduce hospitalisations in those 65 years and older by 73 to 84% (compared with no booster). They are also expected to be effective against recent strains of the Omicron XBB, which is dominant in the United States now.
“An Israel study including 700,000 participants showed 81% reduction in hospitalisations and 86% reduction of deaths using the bivalent in adults 65 years and older, while data from the CDC in November shows a 13.5-fold reduction in hospitalisations for adults 65 years and older who received a further booster as a bivalent versus those who were unvaccinated. There was a 2.5 fold higher rate among seniors vaccinated but without a bivalent booster.
“There is a clear body of consistent evidence now to show the bivalent’s benefit in a booster dose particularly for high risk individuals, and there is nothing to suggest the bivalent is inferior. All data points to added benefit.”
Conflict of interest statement: Professor Turner is a member of the PITAG immunisation subcommiteee to Pharmac; Chair of NVC – the measles national verification committee for the Ministry of Health; a member of the CVTAG – COVID-19 Technical Advisory Group to the Ministry of Health; and a member of PHEAG – Strategic COVID-19 Public Health Advisory Group to the government. The Immunisation Advisory Centre (IMAC) has a contract with the Ministry of Health to deliver clinical advice, promotion, education and training to the healthcare sector for the national schedule vaccines and COVID-19 vaccines.